Experimental Research CHAPTER5

Research Methods -5 Designed by F.Y.N.  An experiment is a research situation in which at least one independent variable, called the experimental variable, is deliberately manipulated or varied by the researcher.

Research Methods -5 Designed by F.Y.N. 一、 Experimental Design Consider an example. An educational psychologist uses three types of instructions to determine the effects of instruction on performance in solving abstract number problems.

Verbal 20 participants Written 20 participants Combination 20 participants Dependent Variable Type of Instructions Randomly Assigned Number of Correct Solutions Experimental Procedure RG 1 RG 2 RG 3 XVXV XWXW XCXC O1O1 O2O2 O3O3 Experimental Design for the Problem-Solving Experiment

Research Methods -5 Designed by F.Y.N.  An experiment design is the structure by which variables are positioned or arranged in the experiment.

Research Methods -5 Designed by F.Y.N.  Experimental Variables Type of instructional organization Type of materials for concept attainment Drug dosage for experimental Length of time on task with no break Instructional procedure used in teaching history Instructional strategy used in teaching third grade math

Research Methods -5 Designed by F.Y.N. 二、 Criteria for a Well-Designed Experiment 1.Adequate experimental control 2.Lack of artificiality 3.Basis for comparison 4.Adequate information from the data 5.Uncontaminated data 6.No confounding of relevant variables 7.Representativeness 8.Parsimony

Research Methods -5 Designed by F.Y.N. 三、 Experimental Validity  The criteria of a well-designed experiment can be summarized as the characteristics that enhance experimental validity.

Research Methods -5 Designed by F.Y.N.  Experimental validity is of four types: Internal validity is concerned with whether changes in the dependent variable are due to the experimental variable. External validity deals with the extent of generalizability of the results. Construct validity is about clear and unambiguous identification of the constructs of the independent and the dependent variables. Statistical conclusion validity deals with the accuracy of the decision about whether the experimental and control groups differ. 三、 Experimental Validity

Research Methods -5 Designed by F.Y.N.  Threats to Experimental Validity: 三、 Experimental Validity Experimental validity must be considered in the context of each specific experiment. Attaining validity is not an all-or-nothing outcome. Possible limits to validity should be recognized and countered through the design and the way the experiment is conducted.

Research Methods -5 Designed by F.Y.N. 四、 Posttest-only Control Group Design The posttest-only control group design contains as many groups as there are experimental treatments, plus a control or comparison group. Subjects are measured only after the experimental treatments have been applied.

Research Methods -5 Designed by F.Y.N. 四、 Posttest-only Control Group Design In the more general sense, the posttest-only control group design can be diagrammed as follows: R G 1 R G 2 R G k R G k+1 …… X1X1 X2X2 XKXK __ O1O1 O2O2 OKOK O K+1 ……

Research Methods -5 Designed by F.Y.N. 五、 Pretest-posttest Control Group Design The pretest-posttest control group design contains as many groups as there are experimental treatments, plus a control group. Subjects are measured before and after receiving the experimental treatments.

Research Methods -5 Designed by F.Y.N. The pretest-posttest control group design can be extended to include more than two groups. It can be diagrammed in general from as follows: R G 1 R G 2 R G k R G k+1 …… X1X1 X2X2 XKXK __ O2O2 O4O4 O 2K O 2(K+1) …… 五、 Pretest-posttest Control Group Design O1O1 O3O3 O 2k-1 O 2k+1 ……

Research Methods -5 Designed by F.Y.N. Exercises Discuss in detail an example of an experiment for which the posttest-only control group is appropriate. Consider such points as why you would not need pretests and the number you would include.

Research Methods -5 Designed by F.Y.N. References Campbell, D.T., and Stanley, J.C. (1963). Experimental and quasi-experimental designs for research on teaching. In N.L. Gage (Ed.), Handbook of research on teaching (pp ). Chicago: Rand McNally. Keppel, G. (1991). Design and analysis: A researcher’s handbook (3rd ed.). Englewood Cliffs, NJ: Prentice-Hall.

Research Methods -5 Designed by F.Y.N. Section II Quasi-Experimental Research

Research Methods -5 Designed by F.Y.N. Quasi-experimental research involves the use of intact groups of subjects in an experiment, rather than assigning subjects at random to experimental treatments.

Research Methods -5 Designed by F.Y.N. 一、 The Problems of Validity Lack of random assignment potentially introduces problems with the validity of the experiment—both internal and external validity.

Research Methods -5 Designed by F.Y.N. When considering problems of validity of quasi- experimental research, limitations should be clearly identified, the equivalence of the groups should be discussed, and possible representativeness and generalizability should be argued on a logical basis. 一、 The Problems of Validity

Research Methods -5 Designed by F.Y.N. 二、 Posttest-only, Nonequivalent Control group Design G1G1 G2G2 GkGk G k+1 …… X1X1 X2X2 XKXK O1O1 O2O2 OKOK O K+1

Research Methods -5 Designed by F.Y.N. 二、 Posttest-only, Nonequivalent Control group Design The posttest-only, nonequivalent control group design contains as many groups as there are experimental treatments, plus a control group. Intact groups are used, and subjects are measured only once, after the experimental treatments have been applied.

Research Methods -5 Designed by F.Y.N. 三、 Pretest-posttest, Nonequivalent Control Group Design G1G1 G2G2 GkGk G k+1 …… X1X1 X2X2 XKXK O2O2 O4O4 O 2k O 2k+2 O1O1 O3O3 O 2k-1 O 2k+1

Research Methods -5 Designed by F.Y.N. 三、 Pretest-posttest, Nonequivalent Control Group Design The pretest-posttest, nonequivalent control group design aids in checking the extent of group similarity, and the pretest scores may be used for statistical control or for generating gain scores.

Research Methods -5 Designed by F.Y.N. 四、 Time Series Designs Time series designs as quasi-experimental designs involves repeated measurement of one or more intact groups, with an experimental treatment inserted between two of the measurements of at least one group.

Research Methods -5 Designed by F.Y.N. 五、 Single-Subject Designs Single-subject designs commonly involve repeated measurement, and they use the single-variable rule--- changing only one variable at a time. A-B A: the baseline condition A-B-A B: the experimental treatment condition A-B-A-B

Research Methods -5 Designed by F.Y.N. Exercises The most desirable procedure for obtaining groups for an experiment is random selection or assignment of subjects, yet at times it is necessary to use intact groups and a quasi-experimental design. Discuss some of the difficulties that may be introduced when intact groups are used.

Research Methods -5 Designed by F.Y.N. References Campbell, D.T., and Stanley, J.C. (1963). Experimental and quasi-experimental designs for research on teaching. In N.L. Gage (Ed.), Handbook of research on teaching (pp ). Chicago: Rand McNally. Meehan, M.L. (1997). Evaluation of the Glenwood getaway from drugs and violence project. Charleston, WV: Appalachia Educational Laboratory.