Experimental Condition Definition
There are many research methods available to the psychological scientist. Some allow researchers to describe phenomena (surveys and observational studies), and another allows researchers to explain phenomena (an experiment). To explain a phenomenon, one must be able to determine cause and effect. The only research method that can do that is an experiment. Scientific experiments are based on observations when a variable has been introduced into a controlled situation. Inferences can be made about the differences between observations and then used to develop theories and to generalize to other similar situations. The controlled situation, in which variables are manipulated and effects measured, comprise the design of the experiment.
In setting up the context, the experimenter must hold as many conditions constant as possible in the situation, while manipulating a variable(s). The variable that is manipulated by the experimenter is called the independent variable (IV); it is free (independent) to be varied by the experimenter. What is being measured is called the dependent variable (DV); it “depends” on the manipulation of the independent variable. Holding conditions constant means making sure that no relevant variable in the experiment is varied besides the IV. The experimental condition is the one in which the IV is presented. The results from this condition can then be contrasted with the results from the control condition, where the IV was not presented. The idea of controlled contrasts is central to experimental design.
Types of Experimental Designs
There are many types of experimental designs. Experimenters may design studies that have one or several independent variables. Similarly, they may have one or several dependent variables. Other variations in experimental design include whether or not the participants are exposed to all manipulations of the IV. If they are, then it is called a within-subjects design. If they only are exposed to one manipulation of the IV, it is called a between-subjects design. The design of the experiment also includes the order of events and how participants are assigned to conditions. Designing an experiment involves a series of decisions and justifications about all of these issues.
An Example of Experimental Condition
A researcher is interested in whether stress causes a decrease in cognitive performance. First, the experimenter must decide what the manipulation will be. The researcher could decide that the IV would be the presentation of a loud tone. This researcher would need to justify (usually through a review of previous literature) that a loud tone is stressful (and he or she would have to specifically define what “loud” meant). Next, the researcher would need to determine what the DV would be, in other words, how would cognitive performance be measured? Percent correct on a math test, or time to complete a puzzle task, could each be a DV. By controlling the presentation of an IV in the experimental condition, the researcher can see its effect on cognitive performance by comparing the findings to those in the control condition. By exerting both types of control (manipulation of the IV, holding conditions constant), any differences in the DV (i.e., differences in scores/time between participants who heard different tones) can be attributed to the manipulation of the IV (the different tones).
- MacLin, M. K., & Solso, R. L. (2007). Experimental psychology: A case approach (8th ed.). Boston: Allyn & Bacon.