Chapter 9 Experimental Research Gay, Mills, and Airasian Educational Research Chapter 9 Experimental Research Gay, Mills, and Airasian

Topics Discussed in this Chapter Defining characteristics of experimental research Conducting experimental research Manipulation and control Threats to validity Internal validity External validity Group designs

Defining Characteristics Research designed to investigate cause and effect relationships through the direct manipulation of an independent variable and control of extraneous variables Independent variable – the variable being manipulated Dependent variable – the variable in which the effect of the manipulation of the independent variable is observed Researcher manipulation and control – choice of treatments, choice of a research design, use of specific procedures, etc. Objectives 1.1 & 1.2

Experimental Process Six steps to conducting experimental research Selection and definition of the problem Statement of a hypothesis indicating a causal relationship between variables Selection of participants and instruments Random selection of a sample of subjects from a larger population Random assignment of members of the sample to each group Selection of valid and reliable instruments Objectives 2.1 & 2.2

Experimental Process Six steps to conducting experimental research (cont.) Selection of a research plan Three types of comparisons Comparison of two different approaches Comparison of new and existing approaches Comparison of different amounts of a single approach Execution of the research plan Two concerns Sufficient exposure to the treatment Substantively different treatments Objectives 2.1, 2.3, & 2.6

Experimental Process Six steps to conducting experimental research (cont.) Analysis of data Formulation of conclusions Objective 2.1

Manipulation and Control The researcher’s decisions related to what constitutes the independent variable Active and assigned variables Active variables are those the researcher actively manipulates Choice of an instructional strategy A particular counseling approach Assigned variables are those that cannot be manipulated by the researcher but are of interest Gender Race Objectives 3.1 & 3.2

Manipulation and Control The researcher’s efforts to remove the influence of any extraneous variables that might have an effect on the dependent variable The goal is to be assured the only differences between groups is that related to the independent variable Participant variables – characteristics of the subjects Pre-existing achievement levels Differences in attitudes Environmental variables – characteristics of the context Learning materials Differences in the time available for treatment between groups Objectives 3.3 & 3.4

Experimental Validity Internal validity – the degree to which the results are attributable to the independent variable and not some other rival explanation External validity – the extent to which the results of a study can be generalized Population validity – generalizations related to other groups of people Ecological validity – generalizations related to other settings, times, contexts, etc. Objectives 4.1, 4.2, 6.1, & 6.2

Experimental Validity Relative importance of internal and external validity Internal and external validity are related reciprocally Controlling internal validity decreases external validity Controlling external validity decreases internal validity First demonstrate an effect in a highly controlled environment (i.e., prioritize internal validity) Second replicate the study in a more realistic, natural setting (i.e., prioritize external validity) Objective 4.3 & 4.4

Threats to Internal Validity History Maturation Testing Instrumentation Statistical regression Differential selection of participants Mortality Selection-maturation interaction, etc. Objectives 5.1 – 5.8

Threats to External Validity Pre-test treatment interaction Multiple treatment interference Selection treatment interaction Specificity of variables Participants Operational definition of the treatment Operational definition of the dependent variable Specific times Specific circumstances Treatment diffusion Objectives 6.3 – 6.7

Threats to External Validity Experimenter effects Reactive arrangements Artificial environment Hawthorne effect John Henry effect Placebo effect Novelty effect Objectives 6.8 & 6.9

Controlling for Extraneous Variables Extraneous variables must be controlled to be able to attribute the effect to the treatment Group equivalency must be assured Four major means to achieve control Randomization Selection – controls for representation Assignment – controls for group equivalency Objectives 2.5, 7.1, & 8.1

Controlling for Extraneous Variables Matching Identifying pairs of subjects “matched” on specific characteristics of interest Randomly assigning subjects from each pair to different groups Difficulty with subjects for whom no match exists Comparing homogeneous groups Restricting subjects to those with similar characteristics Restricting subjects results in problems related to generalization Objectives 8.4 & 8.5

Controlling for Extraneous Variables Using subjects as their own controls Multiple treatments across time Problem with carry-over effects Analysis of covariance (ANCOVA) Statistically adjusting the posttest scores for the subjects in each group for pretest differences that existed at the beginning of the study Creates statistically equivalent groups Objectives 8.6 & 8.7

Controlling for Extraneous Variables Other ways to control extraneous variables Holding variables constant Using only males rather than males and females Selecting teachers with only similar levels of experience Selecting only one grade level Stipulating the specific length of a treatment Objective 8.2

Group Designs Two major classes of group designs Single-variable designs – one independent variable Factorial designs – two or more independent variables Three types of experimental designs Pre-experimental designs Experimental designs Quasi-experimental designs Objectives 9.1, 9.2, 10.1, & 10.2

Pre-Experimental Designs Three types One-shot case study X O One-group pretest-posttest design O X O Static group comparison X1 O X2 O Threats to internal validity – see Figure 9.1 Objective 9.2

True Experimental Designs Three types Pretest-posttest control group design R O X O R O O Posttest only control group design R X O R O Objective 9.4

True Experimental Designs Three types (cont.) Solomon four-group comparison R O X O R O O R X O R O Threats to internal validity – see Figure 9.2 Objective 9.4

Quasi-Experimental Designs Three types Non-equivalent control group design O X O O O Time series design O O O O X O O O O Counterbalanced design O X1 O X2 O X3 O O X3 O X1 O X2 O O X2 O X3 O X1 O Threats to internal validity – see Figure 9.2 Objective 9.5

Factorial Designs Two independent variables and one dependent variable The effect of teaching strategy and gender on students’ achievement The effect of a particular counseling technique and the clients’ ethnicity on the success of the treatment The effect of a specific coaching approach and children in three age groups on the ability to perform certain physical tasks Objective10.1

Factorial Designs This design increases explained variance and reduces unexplained variance Explained variance is that which can be accounted for by the independent variable(s) By adding an additional variable into the design the explained variance is likely going to increase Unexplained variance is that which cannot be accounted for by the independent variable(s) Because it is unexplained, the researcher assumes this is due to error This is also known as error variance Objectives 10.1 & 10.2

Factorial Designs Interaction The degree to which changes in the dependent variable are different depending on the levels of each of the independent variables A particular instructional strategy is more effective for males than females A particular counseling technique is more effective when the ethnicity of the counselor and client are similar Objective 11.1

Factorial Designs Interaction Visually explained by a graph of performance of all levels of both independent variables Parallel lines indicate no interaction Non-parallel lines indicate an interaction Statistically examined with an F-test of the statistical significance of the interaction Objective 11.1

Factorial Designs Interaction Visual presentation of a significant interaction Statistical analysis of this significant interaction: F1,16 = 4.88 (p = .0420) Objective 11.1

Factorial Designs Interaction Visual presentation of a non-significant interaction Statistical analysis of this non-significant interaction: F1,16 = 0.97 (p = .340) Objective 11.1