Experimental Research

1. Experimental Research EAF 410

2. Unique Features of Experimental Research Attempts to influence a particular variable Manipulate the independent variable Tests hypotheses about cause-and-effect relationships

3. Basic Procedure for Experimental Research Construct a hypothesis stating relationship between independent and dependent variables. Determine appropriate treatment for testing hypothesis. Randomly assign individuals to groups.

4. Basic Procedure for Experimental Research Administer treatment. Observe or measure groups receiving different treatments. Determine effect of treatment.

5. Sample Topics Student behavior as effected by teacher bonding strategies in an elementary school. How teacher questioning strategies affect student comprehension. How instructional strategies affect student achievement.

6. Two Basic Conditions of Formal Experiments 1. At least two (but often more) conditions or methods are compared to assess the effect(s) of particular conditions or “treatments” (the independent variable).

7. Two Basic Conditions of Formal Experiments 2. The independent variable is directly manipulated by the researcher -- change is planned for and deliberately manipulated in order to study its effect(s) on one or more outcomes (dependent variable).

8. Characteristics of Experimental Research Comparison of groups Manipulation of the independent variable Randomization

9. Two Groups The Experimental Group Receives some form of treatment. The Control Group Receives no treatment. The Comparison Group Receives a different treatment from the Experimental Group -- can take the place of the Control Group.

10. Manipulation of the Independent Variable The researcher deliberately and directly determines what forms the independent variable will take and then which group will get which form. Independent variables that can be manipulated: Teaching method Assignments Type of counseling Materials Learning activities

11. Establishing the Independent Variable 1) One form of the variable versus another form. A study comparing the inquiry method with the lecture method of instruction in teaching chemistry.

12. Establishing the Independent Variable 2) Presence versus absence of the same form. A study comparing the use of transparencies versus no transparencies in teaching statistics.

13. Establishing the Independent Variable 3) Varying degrees of the same form. A study comparing the effects of different specified amounts of teacher enthusiasm on student attitudes toward mathematics.

14. Randomization Random Assignment Every individual who is participating in the experiment has an equal chance of being assigned to any of the experimental or control conditions. Random Selection Every member of a population has an equal chance of being selected to be a member of the sample.

15. Random Assignment Takes place before the experiment begins. A process of assigning or distributing students to groups, not a result of such distribution. The researcher forms groups that are equivalent -- differ only by chance in any variables of interest.

16. Control of Extraneous Variables Randomization If enough subjects are randomly assigned to each group, researchers can assume the groups are equivalent. Hold Certain Variables Constant The researcher eliminates the possible effects from a variable by removing it from the study.

17. Control of Extraneous Variables Build the Variable Into the Design The researcher includes the variable(s) in the study in order to assess its(their) effects -- exact opposite of previous idea. Matching Pairs of subjects which share certain characteristics are separated into the different groups.

18. Control of Extraneous Variables Use Subjects as Their Own Controls Each subject is exposed to all treatments, and each performance is compared. Analysis of Covariance Variations in the pretest are used to statistically equate groups -- the pretest variances are figured into the posttest scores.

19. Experimental Research Designs Weak -- no built-in controls for internal validity One-Shot Case Study A single group is exposed to a treatment or event, and then a dependent variable is measured to assess the effect. No control group, no comparison, no pretest

20. Experimental Research Designs Weak -- no built-in controls for internal validity One-Group Pretest-Posttest Design No control/comparison group A single group is measured before and after being exposed to treatment of some sort.

21. Experimental Research Designs Weak -- no built-in controls for internal validity Static-Group Comparison Design Two already-existing groups are used, and comparisons are made between them. No pretest, vulnerable to differential subject characteristics

22. Experimental Research Designs Weak -- no built-in controls for internal validity Static-Group Pretest-Posttest Design Two already-existing groups are given a pretest, differential treatment, and a posttest in order to be compared. Subject gain (posttest minus pretest) is analyzed, but still subject to subject characteristics

23. Experimental Research Design, True Experimental Designs Randomized Posttest-Only Control Group Design Two randomly assigned groups are formed, one of which receives treatment and the other does not. Both are posttested. Randomized Pretest-Posttest Control Group Design Same as previous design, except for use of a pretest.

24. Experimental Research Design, True Experimental Designs Randomized Solomon Four-Group Design Four groups of randomly assigned subjects, of which two groups are pretested and two are not. One of the pretested and one of the unpretested groups is exposed to the treatment. All four groups are posttested.

25. Experimental Research Design, True Experimental Designs Random Assignment with Matching Pairs of individuals matched on certain variables to help ensure group equivalence on these variables. The members of each matched pair are assigned to experimental and control groups at random. Works for posttest-only & pretest-posttest control group designs.

26. Types of Matching Mechanical Process of pairing two persons whose scores on a particular variable are similar. Difficult to match on more than two or three variables In order to match, some subjects eliminated from study

27. Types of Matching Statistical Each subject is given a predicted score on the dependent variable, based on the correlation between the dependet variable and the matching variable. The difference between predicted and actual scores used for group comparison.

28. Quasi-Experimental Designs Matching-Only Design Subjects in existing groups are matched. Counterbalanced Designs Each group is exposed to all treatments but in a different order.

29. Quasi-Experimental Designs Time-Series Designs Repeated measurements over a period of time both before and after treatment.

30. Factoral Designs Extends the number of relationships that may be examined in an experimental study. For example, a study of the effectiveness of inquiry and lecture methods on achievement in history -- the researcher might want to include class size as a moderator variable. Moderator variables are either treatment variables or subject characteristic variables that might moderate other variables.

31. Evaluating Threats to Internal Validity in Experimental Studies What specific factors either are known to affect the dependent variable or may logically be expected to affect this variable? What is the likelihood of the comparison groups differing on each of these factors? Evaluate the threats on the basis of how likely they are to have an effect and plan to control for them. If a given threat cannot be controlled, this should be acknowledged.