1. What are the AP Readers Looking
For?
Sessions III & IV

2. Describing a Distribution
Discuss center, shape, and spread in context.
Center: Mean or Median
Shape: Roughly Symmetrical, Right or Left
Skewed
Spread: Standard Deviation, IQR, Range, or
Spread

3. Linear Regression
 Don’t forget about formulas on chart.
 r is the correlation coefficient.
 r^2 is the coefficient of determination.
 r has no units
 Strong r indicates association, not causation.
 r is not affected if x & y are reversed or if
operations (mult, divide, add, sub) are
performed on each x or on each y.
( ) ˆ, is always onx y y a bx= +

4. Linear Regression
 r^2 describes the percent variation of the response
variable, y, explained by the linear relationship
(LSRL) with the explanatory variable, x. PUT IN
CONTEXT!
 When discussing r, describe line as weak,
moderate, or strong linear relationship between x &
y (in context).
 Interpret slope by saying…For every one unit
increase in the explanatory variable, the response
variable increases/decreases by about “b” units.

5. Experimental Design
 Randomization – what to say
 Blocking – always say why
 Avoid use of terms confounding & bias
 Bias is never eliminated only reduced
 Why do we randomize?

6. 2007 MC Question # 35
 A group of students has 60 houseflies in a
large container and needs to assign 20 to each
of three groups labeled A, B, and C for an
experiment. They can capture the flies one at
a time when the flies enter a side chamber in
the container that is baited with food. Which of
the following methods will be most likely to
result in three comparable groups of 20
houseflies each? See handout

7. Experimental Design
 Completely randomized design
– Randomly sort to treatment groups
– Identify treatment groups by name
– State what is to be measured

8. Double Blind
 Neither the participant nor the person who is
evaluating the results is aware of who is getting
the treatment.

9. Blocking
 We block to create homogenous groups
– Blocking reduces variation
– When variation is reduced, the standard deviation of
the responses decreases.
– We can more readily see the effects of the
treatment.

10. Probability Questions
 Show as much work as possible to justify your
answers
 Link answers to work
 “Calculator speak” is ok, but not enough to
justify your answer.
 What do you do if you can’t figure out the
answer to a probability question and need it to
respond to part b).

11. Scoring a Significance Test
 1 pt for the null and alternative hypotheses &
defining the parameter.
 1 pt for assumptions & either the test statistic
and formula OR name of the test

12. Scoring a Significance Test
 1 pt Mechanics; the value of the test statistic &
p-value
 1 pt for decision referencing alpha &
conclusion in context.