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9-1



         Chapter 9

      Hypothesis Testing

                © The McGraw-Hill Companies, Inc., 2000
9-2
      Outline

      
          9-1 Introduction
      
          9-2 Steps in Hypothesis Testing
         9-3 Large Sample Mean Test
         9-4 Small Sample Mean Test
      
          9-5 Proportion Test
                             © The McGraw-Hill Companies, Inc., 2000
9-3
      Outline

      
          9-6 Variance or Standard
              Deviation Test
      
          9-7 Confidence Intervals and
              Hypothesis Testing


                           © The McGraw-Hill Companies, Inc., 2000
9-4
      Objectives
      
        Understand the definitions used
        in hypothesis testing.
      
        State the null and alternative
        hypotheses.
      
        Find critical values for the z test.


                            © The McGraw-Hill Companies, Inc., 2000
9-5
      Objectives
      
        State the five steps used in
        hypothesis testing.
      
        Test means for large samples
        using the z test.
      
        Test means for small samples
        using the t test.

                         © The McGraw-Hill Companies, Inc., 2000
9-6
      Objectives
      
        Test proportions using the z test.
      
        Test variances or standard
        deviation using the chi-square
        test.
      
        Test hypotheses using
        confidence intervals.

                          © The McGraw-Hill Companies, Inc., 2000
9-7
      9-2 Steps in Hypothesis Testing
         A Statistical hypothesis is a conjecture
          about a population parameter. This
          conjecture may or may not be true.
         The null hypothesis, symbolized by H0,
                    hypothesis
          is a statistical hypothesis that states
          that there is no difference between a
          parameter and a specific value or that
          there is no difference between two
          parameters.
                                © The McGraw-Hill Companies, Inc., 2000
9-8
      9-2 Steps in Hypothesis Testing

      
          The alternative hypothesis,
                           hypothesis
          symbolized by H1, is a statistical
          hypothesis that states a specific
          difference between a parameter
          and a specific value or states
          that there is a difference between
          two parameters.
                            © The McGraw-Hill Companies, Inc., 2000
9-9
      9-2 Steps in Hypothesis Testing -
          Example

         A medical researcher is interested in
          finding out whether a new medication
          will have any undesirable side effects.
          The researcher is particularly concerned
          with the pulse rate of the patients who
          take the medication.



                                © The McGraw-Hill Companies, Inc., 2000
9-10
       9-2 Steps in Hypothesis Testing -
           Example

          What are the hypotheses to test whether
           the pulse rate will be different from the
           mean pulse rate of 82 beats per minute?
          H0: µ = 82     H1: µ ≠ 82
       
           This is a two-tailed test.


                                 © The McGraw-Hill Companies, Inc., 2000
9-11
       9-2 Steps in Hypothesis Testing -
           Example

          A chemist invents an additive to
           increase the life of an automobile
           battery. If the mean lifetime of the
           battery is 36 months, then his
           hypotheses are
          H0: µ ≤ 36       H1: µ > 36
          This is a right-tailed test.
                                  © The McGraw-Hill Companies, Inc., 2000
9-12
       9-2 Steps in Hypothesis Testing -
           Example

       
           A contractor wishes to lower heating
           bills by using a special type of
           insulation in houses. If the average of
           the monthly heating bills is $78, her
           hypotheses about heating costs will be
          H0: µ ≥ $78     H0: µ < $78
          This is a left-tailed test.
                                 © The McGraw-Hill Companies, Inc., 2000
9-13   9-2 Steps in Hypothesis Testing

       
           A statistical test uses the data
           obtained from a sample to make
           a decision about whether or not
           the null hypothesis should be
           rejected.


                             © The McGraw-Hill Companies, Inc., 2000
9-14
       9-2 Steps in Hypothesis Testing

        The numerical value obtained
         from a statistical test is called
         the test value.
                  value
       
         In the hypothesis-testing
         situation, there are four possible
         outcomes.

                            © The McGraw-Hill Companies, Inc., 2000
9-15
       9-2 Steps in Hypothesis Testing

          In reality, the null hypothesis
           may or may not be true, and a
           decision is made to reject or not
           to reject it on the basis of the
           data obtained from a sample.


                             © The McGraw-Hill Companies, Inc., 2000
9-16
        9-2 Steps in Hypothesis Testing

                  H0 True          H0 False
                Error
                 Error      Correct
                             Correct
       Reject   Type II
                Type        decision
                            decision
       H0
                Correct
                 Correct       Error
                               Error
       Do not
                decision
                decision      Type II
                              Type II
       reject
       H0
                            © The McGraw-Hill Companies, Inc., 2000
9-17
       9-2 Steps in Hypothesis Testing

       
         A type I error occurs if one
         rejects the null hypothesis when
         it is true.
        A type II error occurs if one does

         not reject the null hypothesis
         when it is false.

                           © The McGraw-Hill Companies, Inc., 2000
9-18
       9-2 Steps in Hypothesis Testing

       
           The level of significance is the
           maximum probability of committing
           a type I error. This probability is
           symbolized by α (Greek letter
           alpha). That is, P(type I error)=α .
       
           P(type II error) = β (Greek letter
           beta).
                               © The McGraw-Hill Companies, Inc., 2000
9-19
       9-2 Steps in Hypothesis Testing

       
           Typical significance levels are:
           0.10, 0.05, and 0.01.
       
           For example, when α = 0.10, there
           is a 10% chance of rejecting a true
           null hypothesis.


                              © The McGraw-Hill Companies, Inc., 2000
9-20
       9-2 Steps in Hypothesis Testing

       
           The critical value(s) separates the
           critical region from the noncritical
           region.
       
           The symbol for critical value is
           C.V.


                               © The McGraw-Hill Companies, Inc., 2000
9-21
       9-2 Steps in Hypothesis Testing

       
           The critical or rejection region is
           the range of values of the test
           value that indicates that there is a
           significant difference and that the
           null hypothesis should be
           rejected.

                               © The McGraw-Hill Companies, Inc., 2000
9-22
       9-2 Steps in Hypothesis Testing

       
           The noncritical or nonrejection
           region is the range of values of
           the test value that indicates that
           the difference was probably due
           to chance and that the null
           hypothesis should not be
           rejected.
                               © The McGraw-Hill Companies, Inc., 2000
9-23
       9-2 Steps in Hypothesis Testing

       
           A one-tailed test (right or left)
           indicates that the null hypothesis
           should be rejected when the test
           value is in the critical region on
           one side of the mean.



                              © The McGraw-Hill Companies, Inc., 2000
9-24
       9-2 Finding the Critical Value for
           α = 0.01 (Right-Tailed Test)


                                         Critical
                       0.9900            region

                      Noncritical
                      region                      α = 0.01
                             0.4900


                         0        z = 2.33


                                 © The McGraw-Hill Companies, Inc., 2000
9-25
       9-2 Finding the Critical Value for
           α = 0.01 (Left-Tailed Test)

          For a left-tailed test when
           α = 0.01, the critical value will be
              –2.33 and the critical region
           will be to the left of –2.33.



                               © The McGraw-Hill Companies, Inc., 2000
9-26
       9-2 Finding the Critical Value for
           α = 0.01 (Two-Tailed Test)

          In a two-tailed test, the null
           hypothesis should be rejected
           when the test value is in either
           of the two critical regions.



                              © The McGraw-Hill Companies, Inc., 2000
9-27
       9-2 Finding the Critical Value for
           α = 0.01 (Two-Tailed Test)


                     α /2 = 0.005
                                                           Critical
          Critical                   0.9900                region
          region
                                    Noncritical
                                    region                     α /2 = 0.005




                      z = –2.58        0          z = 2.58


                                                  © The McGraw-Hill Companies, Inc., 2000
9-28
       9-3 Large Sample Mean Test

       
         The z test is a statistical test for
         the mean of a population. It can
         be used when n ≥ 30, or when
         the population is normally
         distributed and σ is known.
       
         The formula for the z test is
         given on the next slide.
                             © The McGraw-Hill Companies, Inc., 2000
9-29
       9-3 Large Sample Mean Test
                       X −µ
                    z=
                       σ √n
          where
           X = sample mean
           µ = hypothesized population mean
           σ = population deviation
           n = sample size
                               © The McGraw-Hill Companies, Inc., 2000
9-30
       9-3 Large Sample Mean Test -
           Example

          A researcher reports that the average
           salary of assistant professors is more
           than $42,000. A sample of 30 assistant
           professors has a mean salary of
           $43,260. At α = 0.05, test the claim that
           assistant professors earn more than
           $42,000 a year. The standard deviation
           of the population is $5230.

                                  © The McGraw-Hill Companies, Inc., 2000
9-31
       9-3 Large Sample Mean Test -
           Example

       
           Step 1: State the hypotheses and
           identify the claim.
          H0: µ ≤ $42,000 H1: µ > $42,000 (claim)
          Step 2: Find the critical value. Since
           α = 0.05 and the test is a right-tailed
           test, the critical value is z = +1.65.
       
           Step 3: Compute the test value.

                                   © The McGraw-Hill Companies, Inc., 2000
9-32
       9-3 Large Sample Mean Test -
           Example

       
           Step 3: z = [43,260 – 42,000]/[5230/√30]
           = 1.32.
          Step 4: Make the decision. Since the
           test value, +1.32, is less than the critical
           value, +1.65, and not in the critical
           region, the decision is “Do not reject the
           null hypothesis.”


                                   © The McGraw-Hill Companies, Inc., 2000
9-33
       9-3 Large Sample Mean Test -
           Example

       
           Step 5: Summarize the results. There is
           not enough evidence to support the
           claim that assistant professors earn
           more on average than $42,000 a year.
          See the next slide for the figure.




                                 © The McGraw-Hill Companies, Inc., 2000
9-34
       9-3 Large Sample Mean Test -
           Example



                           1.65
                                     Reject
                                    α = 0.05


                        1.32

                          © The McGraw-Hill Companies, Inc., 2000
9-35
       9-3 Large Sample Mean Test -
           Example

          A national magazine claims that the
           average college student watches less
           television than the general public. The
           national average is 29.4 hours per week,
           with a standard deviation of 2 hours. A
           sample of 30 college students has a
           mean of 27 hours. Is there enough
           evidence to support the claim at
           α = 0.01?
                                 © The McGraw-Hill Companies, Inc., 2000
9-36
       9-3 Large Sample Mean Test -
           Example

       
           Step 1: State the hypotheses and
           identify the claim.
          H0: µ ≥ 29.4    H1: µ < 29.4 (claim)
          Step 2: Find the critical value. Since
           α = 0.01 and the test is a left-tailed test,
           the critical value is z = –2.33.
       
           Step 3: Compute the test value.

                                    © The McGraw-Hill Companies, Inc., 2000
9-37
       9-3 Large Sample Mean Test -
           Example

       
           Step 3: z = [27– 29.4]/[2/√30] = – 6.57.
          Step 4: Make the decision. Since the
           test value, – 6.57, falls in the critical
           region, the decision is to reject the null
           hypothesis.




                                   © The McGraw-Hill Companies, Inc., 2000
9-38
       9-3 Large Sample Mean Test -
           Example

       
           Step 5: Summarize the results. There is
           enough evidence to support the claim
           that college students watch less
           television than the general public.
          See the next slide for the figure.




                                 © The McGraw-Hill Companies, Inc., 2000
9-39
       9-3 Large Sample Mean Test -
           Example



                  -6.57

         Reject



                     -2.33

                             © The McGraw-Hill Companies, Inc., 2000
9-40
       9-3 Large Sample Mean Test -
           Example

          The Medical Rehabilitation Education
           Foundation reports that the average
           cost of rehabilitation for stroke victims
           is $24,672. To see if the average cost of
           rehabilitation is different at a large
           hospital, a researcher selected a
           random sample of 35 stroke victims and
           found that the average cost of their
           rehabilitation is $25,226.
                                  © The McGraw-Hill Companies, Inc., 2000
9-41
       9-3 Large Sample Mean Test -
           Example

          The standard deviation of the
           population is $3,251. At α = 0.01, can it
           be concluded that the average cost at a
           large hospital is different from $24,672?
          Step 1: State the hypotheses and
           identify the claim.
          H0: µ = $24,672     H1: µ ≠ $24,672 (claim)

                                   © The McGraw-Hill Companies, Inc., 2000
9-42
       9-3 Large Sample Mean Test -
           Example

       
           Step 2: Find the critical values. Since
           α = 0.01 and the test is a two-tailed test,
           the critical values are z = –2.58 and
           +2.58.
          Step 3: Compute the test value.
       
           Step 3: z = [25,226 – 24,672]/[3,251/√35]
           = 1.01.

                                   © The McGraw-Hill Companies, Inc., 2000
9-43
       9-3 Large Sample Mean Test -
           Example

       
           Step 4: Make the decision. Do not reject
           the null hypothesis, since the test value
           falls in the noncritical region.
          Step 5: Summarize the results. There is
           not enough evidence to support the
           claim that the average cost of
           rehabilitation at the large hospital is
           different from $24,672.
                                  © The McGraw-Hill Companies, Inc., 2000
9-44
       9-3 Large Sample Mean Test -
           Example



                          1.01

         Reject                             Reject



                  -2.58       2.58

                           © The McGraw-Hill Companies, Inc., 2000
9-45
       9-3 P-Values
       
           Besides listing an α value, many
           computer statistical packages give a P-
           value for hypothesis tests. The P-value
           is the actual probability of getting the
           sample mean value or a more extreme
           sample mean value in the direction of
           the alternative hypothesis (> or <) if the
           null hypothesis is true.

                                  © The McGraw-Hill Companies, Inc., 2000
9-46
       9-3 P-Values
       
           The P-value is the actual area under the
           standard normal distribution curve (or
           other curve, depending on what
           statistical test is being used)
           representing the probability of a
           particular sample mean or a more
           extreme sample mean occurring if the
           null hypothesis is true.

                                 © The McGraw-Hill Companies, Inc., 2000
9-47   9-3 P-Values - Example

       
           A researcher wishes to test the claim
           that the average age of lifeguards in
           Ocean City is greater than 24 years.
           She selects a sample of 36 guards and
           finds the mean of the sample to be 24.7
           years, with a standard deviation of 2
           years. Is there evidence to support the
           claim at α = 0.05? Find the P-value.

                                 © The McGraw-Hill Companies, Inc., 2000
9-48   9-3 P-Values - Example

          Step 1: State the hypotheses and
           identify the claim.
          H0: µ ≤ 24    H1: µ > 24 (claim)
       
           Step 2: Compute the test value.
                        24.7 − 24
                   z=             = 2.10
                         2 36


                                     © The McGraw-Hill Companies, Inc., 2000
9-49   9-3 P-Values - Example

          Step 3: Using Table E in Appendix C,
           find the corresponding area under the
           normal distribution for z = 2.10. It is
           0.4821
          Step 4: Subtract this value for the area
           from 0.5000 to find the area in the right
           tail.
                0.5000 – 0.4821 = 0.0179
           Hence the P-value is 0.0179.
                                  © The McGraw-Hill Companies, Inc., 2000
9-50   9-3 P-Values - Example

          Step 5: Make the decision. Since the
           P-value is less than 0.05, the decision is
           to reject the null hypothesis.
          Step 6: Summarize the results. There is
           enough evidence to support the claim
           that the average age of lifeguards in
           Ocean City is greater than 24 years.


                                  © The McGraw-Hill Companies, Inc., 2000
9-51   9-3 P-Values - Example


          A researcher claims that the average
           wind speed in a certain city is 8 miles
           per hour. A sample of 32 days has an
           average wind speed of 8.2 miles per
           hour. The standard deviation of the
           sample is 0.6 mile per hour. At α = 0.05,
           is there enough evidence to reject the
           claim? Use the P-value method.
                                  © The McGraw-Hill Companies, Inc., 2000
9-52   9-3 P-Values - Example

          Step 1: State the hypotheses and
           identify the claim.
           H0: µ = 8 (claim)  H1: µ ≠ 8
       
           Step 2: Compute the test value.
                       8.2 − 8
                   z=          = 1.89
                      0.6 32


                                   © The McGraw-Hill Companies, Inc., 2000
9-53   9-3 P-Values - Example

          Step 3: Using table E, find the
           corresponding area for z = 1.89. It is
           0.4706.
          Step 4: Subtract the value from 0.5000.
              0.5000 – 0.4706 = 0.0294




                                 © The McGraw-Hill Companies, Inc., 2000
9-54   9-3 P-Values - Example

       
           Step 5: Make the decision: Since this test
           is two-tailed, the value 0.0294 must be
           doubled; 2(0.0294) = 0.0588. Hence, the
           decision is not to reject the null
           hypothesis, since the P-value is greater
           than 0.05.
          Step 6: Summarize the results. There is not
           enough evidence to reject the claim that
           the average wind speed is 8 miles per hour.
                                   © The McGraw-Hill Companies, Inc., 2000
9-55
       9-4 Small Sample Mean Test

          When the population standard deviation
           is unknown and n < 30, the z test is
           inappropriate for testing hypotheses
           involving means.
       
           The t test is used in this case.
       
           Properties for the t distribution are
           given in Chapter 8.
                                  © The McGraw-Hill Companies, Inc., 2000
9-56
       9-4 Small Sample Mean Test -
           Formula for t test
                         X −µ
                      t=
                         s n
           where
            X = sample mean
            µ = hypothesized population mean
            s = sample standard deviation
            n = sample size
            degrees of freedom = n − 1
                                © The McGraw-Hill Companies, Inc., 2000
9-57
       9-4 Small Sample Mean Test -
           Example

          A job placement director claims that the
           average starting salary for nurses is
           $24,000. A sample of 10 nurses has a
           mean of $23,450 and a standard
           deviation of $400. Is there enough
           evidence to reject the director’s claim at
           α = 0.05?


                                  © The McGraw-Hill Companies, Inc., 2000
9-58
       9-4 Small Sample Mean Test -
           Example

          Step 1: State the hypotheses and
           identify the claim.
          H0: µ = $24,000 (claim) H1: µ ≠ $24,000
       
           Step 2: Find the critical value. Since
           α = 0.05 and the test is a two-tailed test,
           the critical values are t = –2.262 and
           +2.262 with d.f. = 9.

                                   © The McGraw-Hill Companies, Inc., 2000
9-59
       9-4 Small Sample Mean Test -
           Example

          Step 3: Compute the test value.
           t = [23,450 – 24,000]/[400/√10] = – 4.35.
          Step 4: Reject the null hypothesis, since
           – 4.35 < – 2.262.
          Step 5: There is enough evidence to
           reject the claim that the starting salary
           of nurses is $24,000.

                                  © The McGraw-Hill Companies, Inc., 2000
9-60
       9-3 Small Sample Mean Test -
           Example



             −4.35




               –2.262        2.262

                          © The McGraw-Hill Companies, Inc., 2000
9-61
       9-5 Proportion Test

          Since the normal distribution can be
           used to approximate the binomial
           distribution when np ≥ 5 and nq ≥ 5, the
           standard normal distribution can be
           used to test hypotheses for proportions.
          The formula for the z test for
           proportions is given on the next slide.

                                 © The McGraw-Hill Companies, Inc., 2000
9-62
       9-5 Formula for the z Test for
           Proportions


                    X −µ        X − np
                 z=      or z =
                     σ            npq
                 where
                 µ = np
                σ = npq

                            © The McGraw-Hill Companies, Inc., 2000
9-63
       9-5 Proportion Test - Example
       
           An educator estimates that the dropout
           rate for seniors at high schools in Ohio
           is 15%. Last year, 38 seniors from a
           random sample of 200 Ohio seniors
           withdrew. At α = 0.05, is there enough
           evidence to reject the educator’s claim?



                                 © The McGraw-Hill Companies, Inc., 2000
9-64   9-5 Proportion Test - Example

       
           Step 1: State the hypotheses and identify
           the claim.
          H0: p = 0.15 (claim)  H1: p ≠ 0.15
          Step 2: Find the mean and standard
           deviation. µ = np = (200)(0.15) = 30 and
           σ = √(200)(0.15)(0.85) = 5.05.
          Step 3: Find the critical values. Since
           α = 0.05 and the test is two-tailed the
           critical values are z = ±1.96.
                                   © The McGraw-Hill Companies, Inc., 2000
9-65   9-5 Proportion Test - Example

          Step 4: Compute the test value.
           z = [38 – 30]/[5.05] = 1.58.
          Step 5: Do not reject the null
           hypothesis, since the test value falls
           outside the critical region.




                                  © The McGraw-Hill Companies, Inc., 2000
9-66   9-5 Proportion Test - Example

       
           Step 6: Summarize the results. There is
           not enough evidence to reject the claim
           that the dropout rate for seniors in high
           schools in Ohio is 15%.
          Note: For one-tailed test for
           proportions, follow procedures for the
           large sample mean test.


                                  © The McGraw-Hill Companies, Inc., 2000
9-67   9-5 Proportion Test - Example



                         1.58




                 -1.96     1.96

                          © The McGraw-Hill Companies, Inc., 2000
9-68
       9-6 Variance or Standard Deviation
           Test - Formula

                   (n − 1) s
                             2

              χ =  2
                             with d . f .= n –1
                      σ  2



              where
              n = sample size
              σ = population variance
                2




              s = sample variance
               2




                                 © The McGraw-Hill Companies, Inc., 2000
9-69
       9-6 Assumptions for the Chi-Square
           Test for a Single Variance

          The sample must be randomly
           selected from the population.
       
           The population must be normally
           distributed for the variable under
           study.
       
           The observations must be
           independent of each other.

                                © The McGraw-Hill Companies, Inc., 2000
9-70
       9-6 Variance Test - Example
       
           An instructor wishes to see whether the
           variation in scores of the 23 students in
           her class is less than the variance of the
           population. The variance of the class is
           198. Is there enough evidence to
           support the claim that the variation of
           the students is less than the population
           variance (σ 2 = 225) at α = 0.05?

                                  © The McGraw-Hill Companies, Inc., 2000
9-71
       9-6 Variance Test - Example
          Step 1: State the hypotheses and
           identify the claim.
          H0: σ 2 ≥ 225     H1: σ 2 < 225 (claim)
       
           Step 2: Find the critical value. Since
           this test is left-tailed and α = 0.05, use
           the value 1 – 0.05 = 0.95.
           The d.f. = 23 – 1 = 22. Hence, the critical
           value is 12.338.
                                   © The McGraw-Hill Companies, Inc., 2000
9-72
       9-6 Variance Test - Example
          Step 3: Compute the test value.
           χ 2 = (23 – 1)(198)/225 = 19.36.
          Step 4: Make a decision. Do not reject
           the null hypothesis, since the test value
           falls outside the the critical region.




                                  © The McGraw-Hill Companies, Inc., 2000
9-73
       9-6 Variance Test - Example



           0.05



              12.338 19.36


                             © The McGraw-Hill Companies, Inc., 2000
9-74
       9-6 Variance Test
          Note: When the test is two-tailed, you
           will need to find χ 2(left) and χ 2(right)
           and check whether the test value is less
           than χ 2(left) or whether it is greater
           than χ 2(right) in order to reject the null
           hypothesis.



                                   © The McGraw-Hill Companies, Inc., 2000
9-7 Confidence Intervals and
9-75
           Hypothesis Testing - Example

          Sugar is packed in 5-pound bags. An
           inspector suspects the bags may not
           contain 5 pounds. A sample of 50 bags
           produces a mean of 4.6 pounds and a
           standard deviation of 0.7 pound. Is there
           enough evidence to conclude that the
           bags do not contain 5 pounds as stated,
           at α = 0.05? Also, find the 95%
           confidence interval of the true mean.
                                  © The McGraw-Hill Companies, Inc., 2000
9-7 Confidence Intervals and
9-76
           Hypothesis Testing - Example

          H0: µ = 5   H1: µ ≠ 5 (claim)
          The critical values are +1.96 and – 1.96
                               = 4.6 −
                                     5.00 = − 4.04
       
           The test value is z .
                                 0 7 50
          Since – 4.04 < –1.96, the null hypothesis
           is rejected.
       
           There is enough evidence to support the
           claim that the bags do not weigh 5
           pounds.
                                   © The McGraw-Hill Companies, Inc., 2000
9-7 Confidence Intervals and
9-77
           Hypothesis Testing - Example

       
           The 95% confidence interval for the mean is
           given by           s                    s
                  X −z      ⋅     <µ<X+z         ⋅
                       α2 n                  α2 n
                          0.7  < µ < 4.6 + (1.96) 0.7 
             4.6 − (1.96)                             
                            50                     50 
                           4.406 < µ < 4.794
       
           Notice that the 95% confidence interval of µ does
           not contain the hypothesized value µ = 5. Hence,
           there is agreement between the hypothesis test
           and the confidence interval.
                                      © The McGraw-Hill Companies, Inc., 2000

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Chap#9 hypothesis testing (3)

  • 1. 9-1 Chapter 9 Hypothesis Testing © The McGraw-Hill Companies, Inc., 2000
  • 2. 9-2 Outline  9-1 Introduction  9-2 Steps in Hypothesis Testing  9-3 Large Sample Mean Test  9-4 Small Sample Mean Test  9-5 Proportion Test © The McGraw-Hill Companies, Inc., 2000
  • 3. 9-3 Outline  9-6 Variance or Standard Deviation Test  9-7 Confidence Intervals and Hypothesis Testing © The McGraw-Hill Companies, Inc., 2000
  • 4. 9-4 Objectives  Understand the definitions used in hypothesis testing.  State the null and alternative hypotheses.  Find critical values for the z test. © The McGraw-Hill Companies, Inc., 2000
  • 5. 9-5 Objectives  State the five steps used in hypothesis testing.  Test means for large samples using the z test.  Test means for small samples using the t test. © The McGraw-Hill Companies, Inc., 2000
  • 6. 9-6 Objectives  Test proportions using the z test.  Test variances or standard deviation using the chi-square test.  Test hypotheses using confidence intervals. © The McGraw-Hill Companies, Inc., 2000
  • 7. 9-7 9-2 Steps in Hypothesis Testing  A Statistical hypothesis is a conjecture about a population parameter. This conjecture may or may not be true.  The null hypothesis, symbolized by H0, hypothesis is a statistical hypothesis that states that there is no difference between a parameter and a specific value or that there is no difference between two parameters. © The McGraw-Hill Companies, Inc., 2000
  • 8. 9-8 9-2 Steps in Hypothesis Testing  The alternative hypothesis, hypothesis symbolized by H1, is a statistical hypothesis that states a specific difference between a parameter and a specific value or states that there is a difference between two parameters. © The McGraw-Hill Companies, Inc., 2000
  • 9. 9-9 9-2 Steps in Hypothesis Testing - Example  A medical researcher is interested in finding out whether a new medication will have any undesirable side effects. The researcher is particularly concerned with the pulse rate of the patients who take the medication. © The McGraw-Hill Companies, Inc., 2000
  • 10. 9-10 9-2 Steps in Hypothesis Testing - Example  What are the hypotheses to test whether the pulse rate will be different from the mean pulse rate of 82 beats per minute?  H0: µ = 82 H1: µ ≠ 82  This is a two-tailed test. © The McGraw-Hill Companies, Inc., 2000
  • 11. 9-11 9-2 Steps in Hypothesis Testing - Example  A chemist invents an additive to increase the life of an automobile battery. If the mean lifetime of the battery is 36 months, then his hypotheses are  H0: µ ≤ 36 H1: µ > 36  This is a right-tailed test. © The McGraw-Hill Companies, Inc., 2000
  • 12. 9-12 9-2 Steps in Hypothesis Testing - Example  A contractor wishes to lower heating bills by using a special type of insulation in houses. If the average of the monthly heating bills is $78, her hypotheses about heating costs will be  H0: µ ≥ $78 H0: µ < $78  This is a left-tailed test. © The McGraw-Hill Companies, Inc., 2000
  • 13. 9-13 9-2 Steps in Hypothesis Testing  A statistical test uses the data obtained from a sample to make a decision about whether or not the null hypothesis should be rejected. © The McGraw-Hill Companies, Inc., 2000
  • 14. 9-14 9-2 Steps in Hypothesis Testing  The numerical value obtained from a statistical test is called the test value. value  In the hypothesis-testing situation, there are four possible outcomes. © The McGraw-Hill Companies, Inc., 2000
  • 15. 9-15 9-2 Steps in Hypothesis Testing  In reality, the null hypothesis may or may not be true, and a decision is made to reject or not to reject it on the basis of the data obtained from a sample. © The McGraw-Hill Companies, Inc., 2000
  • 16. 9-16 9-2 Steps in Hypothesis Testing H0 True H0 False Error Error Correct Correct Reject Type II Type decision decision H0 Correct Correct Error Error Do not decision decision Type II Type II reject H0 © The McGraw-Hill Companies, Inc., 2000
  • 17. 9-17 9-2 Steps in Hypothesis Testing  A type I error occurs if one rejects the null hypothesis when it is true.  A type II error occurs if one does not reject the null hypothesis when it is false. © The McGraw-Hill Companies, Inc., 2000
  • 18. 9-18 9-2 Steps in Hypothesis Testing  The level of significance is the maximum probability of committing a type I error. This probability is symbolized by α (Greek letter alpha). That is, P(type I error)=α .  P(type II error) = β (Greek letter beta). © The McGraw-Hill Companies, Inc., 2000
  • 19. 9-19 9-2 Steps in Hypothesis Testing  Typical significance levels are: 0.10, 0.05, and 0.01.  For example, when α = 0.10, there is a 10% chance of rejecting a true null hypothesis. © The McGraw-Hill Companies, Inc., 2000
  • 20. 9-20 9-2 Steps in Hypothesis Testing  The critical value(s) separates the critical region from the noncritical region.  The symbol for critical value is C.V. © The McGraw-Hill Companies, Inc., 2000
  • 21. 9-21 9-2 Steps in Hypothesis Testing  The critical or rejection region is the range of values of the test value that indicates that there is a significant difference and that the null hypothesis should be rejected. © The McGraw-Hill Companies, Inc., 2000
  • 22. 9-22 9-2 Steps in Hypothesis Testing  The noncritical or nonrejection region is the range of values of the test value that indicates that the difference was probably due to chance and that the null hypothesis should not be rejected. © The McGraw-Hill Companies, Inc., 2000
  • 23. 9-23 9-2 Steps in Hypothesis Testing  A one-tailed test (right or left) indicates that the null hypothesis should be rejected when the test value is in the critical region on one side of the mean. © The McGraw-Hill Companies, Inc., 2000
  • 24. 9-24 9-2 Finding the Critical Value for α = 0.01 (Right-Tailed Test) Critical 0.9900 region Noncritical region α = 0.01 0.4900 0 z = 2.33 © The McGraw-Hill Companies, Inc., 2000
  • 25. 9-25 9-2 Finding the Critical Value for α = 0.01 (Left-Tailed Test)  For a left-tailed test when α = 0.01, the critical value will be –2.33 and the critical region will be to the left of –2.33. © The McGraw-Hill Companies, Inc., 2000
  • 26. 9-26 9-2 Finding the Critical Value for α = 0.01 (Two-Tailed Test)  In a two-tailed test, the null hypothesis should be rejected when the test value is in either of the two critical regions. © The McGraw-Hill Companies, Inc., 2000
  • 27. 9-27 9-2 Finding the Critical Value for α = 0.01 (Two-Tailed Test) α /2 = 0.005 Critical Critical 0.9900 region region Noncritical region α /2 = 0.005 z = –2.58 0 z = 2.58 © The McGraw-Hill Companies, Inc., 2000
  • 28. 9-28 9-3 Large Sample Mean Test  The z test is a statistical test for the mean of a population. It can be used when n ≥ 30, or when the population is normally distributed and σ is known.  The formula for the z test is given on the next slide. © The McGraw-Hill Companies, Inc., 2000
  • 29. 9-29 9-3 Large Sample Mean Test X −µ z= σ √n where X = sample mean µ = hypothesized population mean σ = population deviation n = sample size © The McGraw-Hill Companies, Inc., 2000
  • 30. 9-30 9-3 Large Sample Mean Test - Example  A researcher reports that the average salary of assistant professors is more than $42,000. A sample of 30 assistant professors has a mean salary of $43,260. At α = 0.05, test the claim that assistant professors earn more than $42,000 a year. The standard deviation of the population is $5230. © The McGraw-Hill Companies, Inc., 2000
  • 31. 9-31 9-3 Large Sample Mean Test - Example  Step 1: State the hypotheses and identify the claim.  H0: µ ≤ $42,000 H1: µ > $42,000 (claim)  Step 2: Find the critical value. Since α = 0.05 and the test is a right-tailed test, the critical value is z = +1.65.  Step 3: Compute the test value. © The McGraw-Hill Companies, Inc., 2000
  • 32. 9-32 9-3 Large Sample Mean Test - Example  Step 3: z = [43,260 – 42,000]/[5230/√30] = 1.32.  Step 4: Make the decision. Since the test value, +1.32, is less than the critical value, +1.65, and not in the critical region, the decision is “Do not reject the null hypothesis.” © The McGraw-Hill Companies, Inc., 2000
  • 33. 9-33 9-3 Large Sample Mean Test - Example  Step 5: Summarize the results. There is not enough evidence to support the claim that assistant professors earn more on average than $42,000 a year.  See the next slide for the figure. © The McGraw-Hill Companies, Inc., 2000
  • 34. 9-34 9-3 Large Sample Mean Test - Example 1.65 Reject α = 0.05 1.32 © The McGraw-Hill Companies, Inc., 2000
  • 35. 9-35 9-3 Large Sample Mean Test - Example  A national magazine claims that the average college student watches less television than the general public. The national average is 29.4 hours per week, with a standard deviation of 2 hours. A sample of 30 college students has a mean of 27 hours. Is there enough evidence to support the claim at α = 0.01? © The McGraw-Hill Companies, Inc., 2000
  • 36. 9-36 9-3 Large Sample Mean Test - Example  Step 1: State the hypotheses and identify the claim.  H0: µ ≥ 29.4 H1: µ < 29.4 (claim)  Step 2: Find the critical value. Since α = 0.01 and the test is a left-tailed test, the critical value is z = –2.33.  Step 3: Compute the test value. © The McGraw-Hill Companies, Inc., 2000
  • 37. 9-37 9-3 Large Sample Mean Test - Example  Step 3: z = [27– 29.4]/[2/√30] = – 6.57.  Step 4: Make the decision. Since the test value, – 6.57, falls in the critical region, the decision is to reject the null hypothesis. © The McGraw-Hill Companies, Inc., 2000
  • 38. 9-38 9-3 Large Sample Mean Test - Example  Step 5: Summarize the results. There is enough evidence to support the claim that college students watch less television than the general public.  See the next slide for the figure. © The McGraw-Hill Companies, Inc., 2000
  • 39. 9-39 9-3 Large Sample Mean Test - Example -6.57 Reject -2.33 © The McGraw-Hill Companies, Inc., 2000
  • 40. 9-40 9-3 Large Sample Mean Test - Example  The Medical Rehabilitation Education Foundation reports that the average cost of rehabilitation for stroke victims is $24,672. To see if the average cost of rehabilitation is different at a large hospital, a researcher selected a random sample of 35 stroke victims and found that the average cost of their rehabilitation is $25,226. © The McGraw-Hill Companies, Inc., 2000
  • 41. 9-41 9-3 Large Sample Mean Test - Example  The standard deviation of the population is $3,251. At α = 0.01, can it be concluded that the average cost at a large hospital is different from $24,672?  Step 1: State the hypotheses and identify the claim.  H0: µ = $24,672 H1: µ ≠ $24,672 (claim) © The McGraw-Hill Companies, Inc., 2000
  • 42. 9-42 9-3 Large Sample Mean Test - Example  Step 2: Find the critical values. Since α = 0.01 and the test is a two-tailed test, the critical values are z = –2.58 and +2.58.  Step 3: Compute the test value.  Step 3: z = [25,226 – 24,672]/[3,251/√35] = 1.01. © The McGraw-Hill Companies, Inc., 2000
  • 43. 9-43 9-3 Large Sample Mean Test - Example  Step 4: Make the decision. Do not reject the null hypothesis, since the test value falls in the noncritical region.  Step 5: Summarize the results. There is not enough evidence to support the claim that the average cost of rehabilitation at the large hospital is different from $24,672. © The McGraw-Hill Companies, Inc., 2000
  • 44. 9-44 9-3 Large Sample Mean Test - Example 1.01 Reject Reject -2.58 2.58 © The McGraw-Hill Companies, Inc., 2000
  • 45. 9-45 9-3 P-Values  Besides listing an α value, many computer statistical packages give a P- value for hypothesis tests. The P-value is the actual probability of getting the sample mean value or a more extreme sample mean value in the direction of the alternative hypothesis (> or <) if the null hypothesis is true. © The McGraw-Hill Companies, Inc., 2000
  • 46. 9-46 9-3 P-Values  The P-value is the actual area under the standard normal distribution curve (or other curve, depending on what statistical test is being used) representing the probability of a particular sample mean or a more extreme sample mean occurring if the null hypothesis is true. © The McGraw-Hill Companies, Inc., 2000
  • 47. 9-47 9-3 P-Values - Example  A researcher wishes to test the claim that the average age of lifeguards in Ocean City is greater than 24 years. She selects a sample of 36 guards and finds the mean of the sample to be 24.7 years, with a standard deviation of 2 years. Is there evidence to support the claim at α = 0.05? Find the P-value. © The McGraw-Hill Companies, Inc., 2000
  • 48. 9-48 9-3 P-Values - Example  Step 1: State the hypotheses and identify the claim.  H0: µ ≤ 24 H1: µ > 24 (claim)  Step 2: Compute the test value. 24.7 − 24 z= = 2.10 2 36 © The McGraw-Hill Companies, Inc., 2000
  • 49. 9-49 9-3 P-Values - Example  Step 3: Using Table E in Appendix C, find the corresponding area under the normal distribution for z = 2.10. It is 0.4821  Step 4: Subtract this value for the area from 0.5000 to find the area in the right tail. 0.5000 – 0.4821 = 0.0179 Hence the P-value is 0.0179. © The McGraw-Hill Companies, Inc., 2000
  • 50. 9-50 9-3 P-Values - Example  Step 5: Make the decision. Since the P-value is less than 0.05, the decision is to reject the null hypothesis.  Step 6: Summarize the results. There is enough evidence to support the claim that the average age of lifeguards in Ocean City is greater than 24 years. © The McGraw-Hill Companies, Inc., 2000
  • 51. 9-51 9-3 P-Values - Example  A researcher claims that the average wind speed in a certain city is 8 miles per hour. A sample of 32 days has an average wind speed of 8.2 miles per hour. The standard deviation of the sample is 0.6 mile per hour. At α = 0.05, is there enough evidence to reject the claim? Use the P-value method. © The McGraw-Hill Companies, Inc., 2000
  • 52. 9-52 9-3 P-Values - Example  Step 1: State the hypotheses and identify the claim.  H0: µ = 8 (claim) H1: µ ≠ 8  Step 2: Compute the test value. 8.2 − 8 z= = 1.89 0.6 32 © The McGraw-Hill Companies, Inc., 2000
  • 53. 9-53 9-3 P-Values - Example  Step 3: Using table E, find the corresponding area for z = 1.89. It is 0.4706.  Step 4: Subtract the value from 0.5000. 0.5000 – 0.4706 = 0.0294 © The McGraw-Hill Companies, Inc., 2000
  • 54. 9-54 9-3 P-Values - Example  Step 5: Make the decision: Since this test is two-tailed, the value 0.0294 must be doubled; 2(0.0294) = 0.0588. Hence, the decision is not to reject the null hypothesis, since the P-value is greater than 0.05.  Step 6: Summarize the results. There is not enough evidence to reject the claim that the average wind speed is 8 miles per hour. © The McGraw-Hill Companies, Inc., 2000
  • 55. 9-55 9-4 Small Sample Mean Test  When the population standard deviation is unknown and n < 30, the z test is inappropriate for testing hypotheses involving means.  The t test is used in this case.  Properties for the t distribution are given in Chapter 8. © The McGraw-Hill Companies, Inc., 2000
  • 56. 9-56 9-4 Small Sample Mean Test - Formula for t test X −µ t= s n where X = sample mean µ = hypothesized population mean s = sample standard deviation n = sample size degrees of freedom = n − 1 © The McGraw-Hill Companies, Inc., 2000
  • 57. 9-57 9-4 Small Sample Mean Test - Example  A job placement director claims that the average starting salary for nurses is $24,000. A sample of 10 nurses has a mean of $23,450 and a standard deviation of $400. Is there enough evidence to reject the director’s claim at α = 0.05? © The McGraw-Hill Companies, Inc., 2000
  • 58. 9-58 9-4 Small Sample Mean Test - Example  Step 1: State the hypotheses and identify the claim.  H0: µ = $24,000 (claim) H1: µ ≠ $24,000  Step 2: Find the critical value. Since α = 0.05 and the test is a two-tailed test, the critical values are t = –2.262 and +2.262 with d.f. = 9. © The McGraw-Hill Companies, Inc., 2000
  • 59. 9-59 9-4 Small Sample Mean Test - Example  Step 3: Compute the test value. t = [23,450 – 24,000]/[400/√10] = – 4.35.  Step 4: Reject the null hypothesis, since – 4.35 < – 2.262.  Step 5: There is enough evidence to reject the claim that the starting salary of nurses is $24,000. © The McGraw-Hill Companies, Inc., 2000
  • 60. 9-60 9-3 Small Sample Mean Test - Example −4.35 –2.262 2.262 © The McGraw-Hill Companies, Inc., 2000
  • 61. 9-61 9-5 Proportion Test  Since the normal distribution can be used to approximate the binomial distribution when np ≥ 5 and nq ≥ 5, the standard normal distribution can be used to test hypotheses for proportions.  The formula for the z test for proportions is given on the next slide. © The McGraw-Hill Companies, Inc., 2000
  • 62. 9-62 9-5 Formula for the z Test for Proportions X −µ X − np z= or z = σ npq where µ = np σ = npq © The McGraw-Hill Companies, Inc., 2000
  • 63. 9-63 9-5 Proportion Test - Example  An educator estimates that the dropout rate for seniors at high schools in Ohio is 15%. Last year, 38 seniors from a random sample of 200 Ohio seniors withdrew. At α = 0.05, is there enough evidence to reject the educator’s claim? © The McGraw-Hill Companies, Inc., 2000
  • 64. 9-64 9-5 Proportion Test - Example  Step 1: State the hypotheses and identify the claim.  H0: p = 0.15 (claim) H1: p ≠ 0.15  Step 2: Find the mean and standard deviation. µ = np = (200)(0.15) = 30 and σ = √(200)(0.15)(0.85) = 5.05.  Step 3: Find the critical values. Since α = 0.05 and the test is two-tailed the critical values are z = ±1.96. © The McGraw-Hill Companies, Inc., 2000
  • 65. 9-65 9-5 Proportion Test - Example  Step 4: Compute the test value. z = [38 – 30]/[5.05] = 1.58.  Step 5: Do not reject the null hypothesis, since the test value falls outside the critical region. © The McGraw-Hill Companies, Inc., 2000
  • 66. 9-66 9-5 Proportion Test - Example  Step 6: Summarize the results. There is not enough evidence to reject the claim that the dropout rate for seniors in high schools in Ohio is 15%.  Note: For one-tailed test for proportions, follow procedures for the large sample mean test. © The McGraw-Hill Companies, Inc., 2000
  • 67. 9-67 9-5 Proportion Test - Example 1.58 -1.96 1.96 © The McGraw-Hill Companies, Inc., 2000
  • 68. 9-68 9-6 Variance or Standard Deviation Test - Formula (n − 1) s 2 χ = 2 with d . f .= n –1 σ 2 where n = sample size σ = population variance 2 s = sample variance 2 © The McGraw-Hill Companies, Inc., 2000
  • 69. 9-69 9-6 Assumptions for the Chi-Square Test for a Single Variance  The sample must be randomly selected from the population.  The population must be normally distributed for the variable under study.  The observations must be independent of each other. © The McGraw-Hill Companies, Inc., 2000
  • 70. 9-70 9-6 Variance Test - Example  An instructor wishes to see whether the variation in scores of the 23 students in her class is less than the variance of the population. The variance of the class is 198. Is there enough evidence to support the claim that the variation of the students is less than the population variance (σ 2 = 225) at α = 0.05? © The McGraw-Hill Companies, Inc., 2000
  • 71. 9-71 9-6 Variance Test - Example  Step 1: State the hypotheses and identify the claim.  H0: σ 2 ≥ 225 H1: σ 2 < 225 (claim)  Step 2: Find the critical value. Since this test is left-tailed and α = 0.05, use the value 1 – 0.05 = 0.95. The d.f. = 23 – 1 = 22. Hence, the critical value is 12.338. © The McGraw-Hill Companies, Inc., 2000
  • 72. 9-72 9-6 Variance Test - Example  Step 3: Compute the test value. χ 2 = (23 – 1)(198)/225 = 19.36.  Step 4: Make a decision. Do not reject the null hypothesis, since the test value falls outside the the critical region. © The McGraw-Hill Companies, Inc., 2000
  • 73. 9-73 9-6 Variance Test - Example 0.05 12.338 19.36 © The McGraw-Hill Companies, Inc., 2000
  • 74. 9-74 9-6 Variance Test  Note: When the test is two-tailed, you will need to find χ 2(left) and χ 2(right) and check whether the test value is less than χ 2(left) or whether it is greater than χ 2(right) in order to reject the null hypothesis. © The McGraw-Hill Companies, Inc., 2000
  • 75. 9-7 Confidence Intervals and 9-75 Hypothesis Testing - Example  Sugar is packed in 5-pound bags. An inspector suspects the bags may not contain 5 pounds. A sample of 50 bags produces a mean of 4.6 pounds and a standard deviation of 0.7 pound. Is there enough evidence to conclude that the bags do not contain 5 pounds as stated, at α = 0.05? Also, find the 95% confidence interval of the true mean. © The McGraw-Hill Companies, Inc., 2000
  • 76. 9-7 Confidence Intervals and 9-76 Hypothesis Testing - Example  H0: µ = 5 H1: µ ≠ 5 (claim)  The critical values are +1.96 and – 1.96 = 4.6 − 5.00 = − 4.04  The test value is z . 0 7 50  Since – 4.04 < –1.96, the null hypothesis is rejected.  There is enough evidence to support the claim that the bags do not weigh 5 pounds. © The McGraw-Hill Companies, Inc., 2000
  • 77. 9-7 Confidence Intervals and 9-77 Hypothesis Testing - Example  The 95% confidence interval for the mean is given by s s X −z ⋅ <µ<X+z ⋅ α2 n α2 n  0.7  < µ < 4.6 + (1.96) 0.7  4.6 − (1.96)     50   50  4.406 < µ < 4.794  Notice that the 95% confidence interval of µ does not contain the hypothesized value µ = 5. Hence, there is agreement between the hypothesis test and the confidence interval. © The McGraw-Hill Companies, Inc., 2000

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