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Experimental design

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This Power point reveals brief description of experimental designs and types and application.This is useful for beginners in health care professionals

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Experimental design

  1. 1. EXPERIMENTAL DESIGNS COMPLETELY RANDOMIZED DESIGN, RANDOMIZED BLOCK DESIGN, LATIN SQUARE DESIGN , OTHER DESIGNS. D. Kavitha MSc(N); MSc(Psy);BSAM; DHHM Ph.D Scholar
  2. 2. Experimental Research
  3. 3. Research design  It is master plan specifying the methods and procedures for following for collecting and analyzing the needed information in a research study
  4. 4. Experimental research design …the researcher selects participants and divides them into two or more groups having similar characteristics and, then, applies the treatment(s) to the groups and measures the effects upon the groups
  5. 5. Uniqueness of experimental research design • Experimental Research is unique in two important respects: 1) Only type of research that attempts to influence a particular variable 2) Best type of research for testing hypotheses about cause-and-effect relationships • Experimental Research looks at the following variables: • Independent variable (treatment) • Dependent variable (outcome)
  6. 6. Major Characteristics of Experimental Research • The researcher manipulates the independent variable. • They decide the nature and the extent of the treatment. • After the treatment has been administered, researchers observe or measure the groups receiving the treatments to see if they differ. • Experimental research enables researchers to go beyond description and prediction, and attempt to determine what caused effects.
  7. 7. Essential Characteristics of Experimental Research Comparison of Groups: • The experimental group receives a treatment of some sort while the control group receives no treatment. • Enables the researcher to determine whether the treatment has had an effect or whether one treatment is more effective than another. Manipulation of the Independent Variable: • The researcher deliberately and directly determines what forms the independent variable will take and which group will get which form.
  8. 8. Essential Characteristics of Experimental Research Randomization • Random assignment is similar but not identical to random selection. • Random assignment means that every individual who is participating in the experiment has an equal chance of being assigned to any of the experimental or control groups. • Random selection means that every member of a population has an equal chance of being selected to be a member of the sample. • Three things occur with random assignments of subjects: 1) It takes place before the experiment begins 2) Process of assigning the groups takes place 3) Groups should be equivalent
  9. 9. Simple Random Sample  Every subset of a specified size n from the population has an equal chance of being selected
  10. 10. Stratified Random Sample  The population is divided into two or more groups called strata, according to some criterion, such as geographic location, grade level, age, or income, and subsamples are randomly selected from each strata.
  11. 11. Cluster Sample  The population is divided into subgroups (clusters) like families. A simple random sample is taken of the subgroups and then all members of the cluster selected are surveyed.
  12. 12. Systematic Sample  Every kth member ( for example: every 10th person) is selected from a list of all population members.
  13. 13. Types of Designs  The basic structure of a research study . . . particularly relevant to experimental research  Types of experimental designs (Campbell & Stanley, 1963)  Pre-experimental  Quasi-experimental  True experimental
  14. 14. Pre-experimental design Quasi – experimental design True experimental design •One shot case design •One group pretest- posttest design •FEATURES •Manipulation of independent variables •Limited control over the extraneous variables •No randomization and control group •Non randomized block design •Time series design •FEATURES •Manipulation of independent variable •Absence of either randomization/ control group •Post –test only control design •Pre –test– posttest control group design •Factorial design •Randomized block design •Cross over design •FEATURES •Manipulation of independent variable •Presence of control group •Randomization
  15. 15. Variable  a concept (e.g., intelligence, height, aptitude) that can assume any one of a range of values  Independent variable - an activity of characteristic believed to make a difference with respect to some behavior  Ex - experimental variable, active variable, cause, treatment  Dependent variable - the change or difference occurring a result of the independent variable  Ex- Assigned variable, effect, outcome, posttest
  16. 16. Steps in conducting experimental research  Decide if an experiment addresses the research problem  Form hypotheses to test cause-effect relationships  Select an experimental treatment and introduce it  Identify study participants choose a type of experimental design  Conduct the experiment  Organize and analyze the data  Develop an experimental research report
  17. 17.  The concept of validity…the experiment tests the variable(s) that it purports to test  Threats to validity…  Internal: factors other than the independent variable that affect the dependent variable( campbell 1963)  External: factors that affect the generalizability of the study to groups and settings beyond those of the experiment
  18. 18. Threats of internal validity  History  Maturation of subjects  Testing  Instrumentation change  Mortality  Selection bias – maturation interaction
  19. 19. History  Some event beside the experimental treatment occurs during the course of the study , and this event even influence dependent variable.
  20. 20. Maturation of subjects  Experimental research is carried on long period of time over a group of subjects there may be changes in the subjects in different ways.  Increase in height, weight.  Ex. Nutritional protocol on height & weight of malnourished children
  21. 21. Testing  Effect of taking a pretest of subjects’ performance of post test.  The effect of taking a pretest may sensitize an individual and improve the score of the post test.  Individuals generally score higher during second test regardless of treatment.
  22. 22. Instrument change  Changes in instruments, calibration of instruments, observers or scorers may cause changes in the measurements
  23. 23. Mortality  Loss or dropout of the subject during course of the study  The longer period of study the more chance for dropout.  Ex. longitudinal study
  24. 24. Selection bias  Subjects are not selected randomly for participation in groups , there is a possibility of comparison may not equivalent.
  25. 25. External validity  Hawthorne effect  Subjects may behave in particular manner because they are aware that they are being observed
  26. 26. Experimental effect  Threat to study results when researcher’s characteristic , mannerism, behavior may influence subject matter.
  27. 27. Reactive effect of pretest  Effect of pretest occurs when subjects have been sensitized to the treatment because of taking pretest.  Ex – pretest may sensitize to learn about HIV/ AIDS irrespective of health education is provided
  28. 28. Novelty effect: Treatment is new , the subjects and researchers act different ways People : Generalization is not applicable depending upon the race. Place: Generalization not possible for people living in rural and urban area Time : older results can not be generalized over periods of time.
  29. 29. Most common way to eliminate threats  Experimental control Experimental control attempts to predict events that will occur in the experimental setting by neutralizing the effects of other factors.  Physical Control Gives all subjects equal exposure to the independent variable. Controls non-experimental variables that effect the dependent variable.  Selective Control Indirectly manipulate by selecting in or out variables that cannot be controlled  Statistical Control Variables not conducive to physical or selective manipulation may be controlled by statistical techniques.
  30. 30. Criteria for evaluating experimental Research  Does the experiment have a powerful intervention?  Does it employ few treatment groups (e.g. only two)?  Will participant profit from the intervention?  Is there a systematic way the researcher derived the number of participants per group?
  31. 31. Criteria for evaluating experimental Research  Were there an adequate number of participants used in the study?  Were valid, reliable, and sensitive measures or observations used?  Did the study control for extraneous factors?  Did the researcher control for threats to internal validity?
  32. 32. Types of pre experimental design  The One-Shot Case Study  A single measure is recorded after the treatment in administered.  Study lacks any comparison or control of extraneous influences.  To remedy this design, a comparison could be made with another group.  Diagrammed as:
  33. 33. The One-Group Pretest-Posttest Design  Subjects are measured before and after treatment is administered.  Uncontrolled-for threats to internal validity exist.  To remedy this design, a comparison group could be added.  Diagrammed as:
  34. 34. The Static-Group Comparison Design  Use of 2 existing, or intact groups.  Experimental group is measured after being exposed to treatment.  Control group is measured without having been exposed to the treatment.  Diagrammed as:
  35. 35. The Static-Group Pretest-Posttest Design  Pretest is given to both groups.  “Gain” or “change” = pretest score - posttest score.  Better control of subject characteristics threat.  A pretest raises the possibility of a testing threat.
  36. 36. Pre experimental design Advantages Disadvantages Very simple Convenient to conduct in natural settings Suitable for beginners Weak design to establish casual relationship between independent and dependent variable Very little control over the research Higher threat to internal validity
  37. 37. Characteristic of quasi experimental research design  Manipulation of independent variable  Lack of one / two essential character of true experimental design  Quasi independent variable used instead of true independent variable.
  38. 38. Types of quasi experimental design Nonequivalent /Non randomized control group design O X O O O random assignment of intact groups that are pretested ( O ), exposed to a treatment ( X ) and then posttested ( O ) Time-series design O O O O X O O O O a single group is pretested ( O ) repeatedly until pretest scores are stable, exposed to a treatment ( X ) and, then, is repeatedly posttested ( O )
  39. 39. Possible Outcome Patterns in a Time-Series Design
  40. 40. Characteristics of true experimental design  Manipulation – control of independent variable by the researcher through treatment/ intervention  Control – the use of control group and extraneous variables on the dependent variable  Randomization – every subject gets equal chance being assigned to experimental and control group.
  41. 41. Advantages Disadvantage s Most powerful design to establish causal relationship between independent and dependent variable Cannot be replicated in studies conducted in human begins due ethical problems Purity of the observation Many of the human variables neither have valid measurable criteria nor instruments to measure. Create conditions in a short period of time that may take years to occur naturally Studies conducted in hospital / community difficult to control the extraneous variable Conducted in laboratory, experimental unit, specialized research setting Very difficult get co operation for treatment/ intervention
  42. 42. True Experimental • The essential ingredient of a true experiment is random assignment of subjects to treatment groups • Random assignments is a powerful tool for controlling threats to internal validity – The Randomized Posttest-only Control Group Design • Both groups receiving different treatments – The Randomized Pretest-Posttest Control Group Design • Pretest is included in this design – The Randomized Solomon Four-Group Design • Four groups used, with two pre-tested and two not pre-tested
  43. 43. The Randomized Posttest-Only Control Group Design  Experimental group tested after treatment exposure.  Control group tested at the same time without exposure to experimental treatment.  Includes random assignment to groups.  Threats to internal validity – mortality, attitudinal, implementation, data collector bias, location and history.
  44. 44. Example of a Randomized Posttest- Only Control Group Design
  45. 45. The Randomized Pretest- Posttest Control Group Design  Experimental group tested before and after treatment exposure  Control group tested at same two times without exposure to experimental treatment  Includes random assignment to groups.  Pretest raises the possibility of a pretest treatment interaction threat
  46. 46. Example of a Randomized Pretest- Posttest Control Group Design
  47. 47. The Randomized Solomon Four- Group Design  Combines pretest-posttest with control group design and the posttest-only with control group design.  Provides means of controlling the interactive test effect and other sources of extraneous variation.  Does include random assignment.  Weakness: requires a large sample.
  48. 48. Example of a Randomized Solomon Four-Group Design
  49. 49. A Randomized Posttest-Only Control Group Design
  50. 50. Solomon four-group design R O X1 O R O X2 O R X1 O R X2 O four groups are formed by random assignment ( R ) of participants, two groups are pretested ( O ) and two are not, one pretested and one un pretested group receive the experimental treatments ( X1, X2 ), each group is are administered a posttest on the dependent variable, and posttest scores are compared to determine effectiveness of treatments
  51. 51. Factorial design  involve two or more independent variables with at least one independent variable being manipulated by the researcher two-by-two factorial design (four cells) 2 X 2  two types of factors (e.g., method of instruction) each of which has two levels (e.g., traditional vs. innovative)
  52. 52. Using a Factorial Design to Study Effects of Method and Class Size on Achievement
  53. 53. Illustration of Interaction and No Interaction in a 2 by 2 Factorial Design
  54. 54. Example of a 4 by 2 Factorial Design
  55. 55. Randomized block design  Principle of local control along with other two principle of experimental design  subjects are first divided into groups  each group the subjects are relatively homogeneous  The number of the equal in each group  Extraneous variable is fixed
  56. 56. Type of antihypert ensive drugs Blocks Patients with primary hypertension DM patients with hypertension Renal patients with hypertension A A,I B,II A,III B B,I B,II B,III C C,I C,II C,III
  57. 57. Cross over design / repeat measure design  Subjects exposed more than one treatment  Subjects randomly assigned to different orders of treatment  Equal distribution of character among the group
  58. 58. Latin square design  very frequently used in agricultural research.  An experiment has to be made through which the effects of five different varieties of fertilizers on the yield of a certain crop.  out put occur depend on soil not only on the fertilizer  L.S. design is used when there are two major extraneous factors such as the varying soil fertility and varying seeds
  59. 59. Seed Differen ces FERTILITY LEVEL X1 A B C D E X2 B C D E A X3 C D E A B X4 D E A B C X5 E A B C D
  60. 60. Other designs Descriptive design  Univariant descriptive design – the frequency of occurrence of the phenomenon  Ex – the experience of patients suffering from rheumatoid arthritis  Prevalence of vitamin D deficiency among pregnant women  Used to identify, describe the perception, awareness, behavior, attitude, knowledge and practice of people.
  61. 61. Exploratory design  Used to identify , explore and describe the existing phenomenon and its related factors  Ex . contributing factors of sleep disturbance among patients admitted in ICU
  62. 62. Comparative design  Comparing and contrasting two or more sample of subjects on one or more variable  Attributes-Knowledge, perception, attitudes  Physical and psychological symptoms  Ex KAP on Vitamin D among antenatal mothers
  63. 63. Prospective Cohort Study Some have the factor (c) Population (lapse of time) Begin enquiry here & work forwards Sample people without the disease Disease (a) Disease (b) No Disease No Disease Statistic = Relative Risk [RR] = (a/c) divided by (b/d) This shows the ratio of incidence in exposed compared to non-exposed. RR > 1 implies a hazard; RR < 1 implies a protective factor 95% CI are usually presented: e.g., RR = 1.9 (95% CI 1.5, 2.3) Note: as you begin with people who do not have the disease, you can calculate incidence but not prevalence. (Prevalence would be underestimated as you omitted existing cases) Some do not (d) Outcomes
  64. 64. Retrospective Case-Control Study Population Select Cases (have the disease) Sample of Controls (who do not have the disease) Exposed (c) Exposed (a) Not Exposed (d) Not Exposed (b) Begin enquiry here & look backwards Statistic = Odds Ratio [OR] = (a/b) divided by (c/d) This shows how many times more likely were the cases to have been exposed than the controls. OR interpreted in same way as RR Review history Review history Note: as you begin with people who already have the disease, you cannot calculate incidence or prevalence
  65. 65. Developmental research design Cross sectional design  Researcher collect data at particular point of time  Ex –assessing the awareness on swine flu among people of an area Longitudinal design  Collect the extended period of time  follow up studies
  66. 66. Other type of trails  Pilot studies and feasibility studies– run before a large trail take place  Screening trails – cervical cancer screening trail  Prevention trails – breast cancer prevention trail.  Trails looking at causes and patterns of disease  Case control studies  Sequential trails
  67. 67. Conclusion  There are several research designs and the researcher must decide in advance of collection and analysis of data as to which design would prove to be more appropriate for his research project.
  68. 68. Applying What you Have Learned: An Experimental Study Review the article and look for the following:  The research problem and use of quantitative research  Use of the literature  The purpose statement and research hypothesis  Types and procedures of data collection  Types and procedures of data analysis and interpretation  The overall report structure

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