Experimental Design Essay

The purpose of an experiment is to systematically test and prove, or to test and disprove a hypothesis. This is accomplished by collecting evidence, observing the effect of variables, and measuring the results. An experiment is a controlled event used to objectively observe phenomena where one or more variables are used to interact with a constant variable. The researcher observes the outcome of the constant variable on the other variables. The experimenter is interested in establishing causality through isolation of the causal effects and providing evidence. The independent variable is assumed to cause the change in the other variables and is therefore manipulated by the researcher. The dependent variable is influenced by one or more

The experimental design utilizes control techniques, the use of randomization, and replication in an attempt to identify sources of variability in the experimental unit. The advantage of using experimental design methods in performing a study is its strength in maintaining strong internal validity. Experimental designs are often touted as the most rigorous of all research designs or as the gold standard against which all other designs are judged (Trochim & Donnelly, 2008). A disadvantage of using experimental design methods resides in the introduction of reflective, expectancy, or casual bias.

Internal validity refers to the accuracy of conclusions about cause and effect (Cozby & Bates, 2012). An experimental design is said to have strong internal validity when the results can be attributed to the effects of the independent variable. To achieve internal validity, the researcher must design and conduct the experiment so that the only reasonable cause of the results, is the manipulation of the independent variable. This paper shall address the components and the issues commonly confronted when structuring an experimental

Possible confounds in this study include the history effect, attrition, and possibly subject effects, as well.

4. Internal validity represents the approximate truth of inferences regarding cause-effect or causal relationships (Trochim & Donnelly, 2008, p. 186). External validity concerns the applicability of generalization or replication of the study results. Internal and external validity is important to researchers because without internal validity, the researcher cannot prove cause and effect. Without external validity, the research design cannot be generalized or replicated.

6. In a within-subjects design, all participants receive the same treatment and the same participants are used in all experimental conditions. In a matched-subjects design, subjects are randomly assigned and the researcher will use a separate but equal experimental group that is matched on relevant variables. Groups in both designs are fairly equivalent and statistically, a within-subjects and matched-subjects research design is more powerful. Both designs practically eliminate the chance of individual bias affecting the results.