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Experimental Research - Coggle Diagram

- - - - Experimental research is best suited for explanatory research (rather than for descriptive or exploratory research), where the goal of the study is to examine cause-effect relationships.
        
        Laboratory experiments, conducted in laboratory (artificial) settings, tend to be high in internal validity, but this comes at the cost of low external validity (generalizability), because the artificial (laboratory) setting in which the study is conducted may not reflect the real world.
        
        Field experiments, conducted in field
        settings such as in a real organization, and high in both internal and external validity.
        
        Experimental research can be grouped into two broad categories: true experimental designs and quasi-experimental designs.
        
        Both designs require treatment manipulation, but
        while true experiments also require random assignment, quasi-experiments do not.
- - - - Any measurements conducted before the treatment is administered are called pretest measures, while those conducted after the treatment are posttest measures.
        
        Random selection is the process of randomly
        drawing a sample from a population or a sampling frame.
        
        This approach is typically employed in survey research and assures that each unit in the population has a positive chance of being selected into the sample.
        
        Random assignment is however a process of randomly assigning
        subjects to experimental or control groups.
        
        Threats to internal validity.
        
        History threat is the possibility that the observed effects (dependent variables) are caused by extraneous or historical events rather than by the experimental treatment.
        
        Maturation threat refers to the possibility that observed effects are caused by natural maturation of subjects rather than the experimental treatment.
        
        Testing threat is a threat in pre-post designs where subjects' posttest responses are conditioned by their pretest responses.
        
        Instrumentation threat, which also occurs in pre-post designs, refers to the possibility that the difference between pretest and posttest scores is not due to the remedial math program, but due to changes in the administered test, such as the posttest having a higher or lower degree of difficulty than the pretest.
        
        Mortality threat refers to the possibility that subjects may be dropping out of the study at differential rates between the treatment and control groups due to a systematic reason, such that the dropouts were mostly students who scored low on the pretest.
        
        Regression threat, also called a regression to the mean, refers to the statistical tendency of a group's overall performance on a measure during a posttest to regress toward the mean of that measure rather than in the anticipated direction.
- - - - Posttest-only control group design. This design is a simpler version of the pretest-posttest design where pretest measurements are omitted.
        
        Sometimes, measures of dependent variables may be influenced by extraneous variables called covariates. Covariates are those variables that are not of central interest to an experimental study but should nevertheless be controlled in an experimental design in order to eliminate their potential effect on the dependent variable and therefore allow for a more accurate detection of the effects of the independent variables of interest.
        
        In a factorial design, a main effect is said to exist if the dependent variable shows a significant difference between multiple levels of one factor, at all levels of other factors.
        
        An interaction effect exists when the
        effect of differences in one factor depends upon the level of a second factor.
- - - - Switched replication design. This is a two-group design implemented in two phases with three waves of measurement.
        
        Quasi-experimental designs are almost identical to true experimental designs but lacking one key ingredient: random assignment.
        
        Regression-discontinuity (RD) design. This is a non-equivalent pretest-posttest design where subjects are assigned to treatment or control group based on a cutoff score on a preprogram measure.
        
        Experimental research is one of the most difficult of research designs and should not be taken lightly.
        
        This type of research is often best with a multitude of methodological problems.
        
        Second, many of the measurement instruments used in experimental research are not tested for reliability and validity, and are incomparable across studies.
        
        Third, many experimental research use inappropriate research designs, such as irrelevant dependent variables, no interaction effects, no experimental controls, and non-equivalent stimulus across treatment groups.
        
        First, though experimental research requires theories for framing hypotheses for testing, much of current experimental research is atheoretical.