The hypothesis is true if independent variable produces lawful changes in dependent variable (Mcguigan, 1993). Independent variable is a stimulus or circumstance presented in the experiment and is manipulated by experimenters. The response or participant’s behavior change which the experimenters measured is the dependent variable (Liebert, 1995). The stimulus-response relationship may influences by extraneous variable that operates in the experiment in addition to the independent variable, causing incorrectness of data. Since data collected indicates the true or false probability of hypothesis, extraneous variable must be eliminated or regulated by a control group. Independent variable is controlled when varied in a known and specified manner.
Typically, participants are assigned to 2 groups: experimental group and control group by randomization. This balances conditions of the 2 groups, letting them approximately equivalent (Mcguigan, 1993). The experimental group exposed to experimental treatment whilst control group exposed to normal treatment. The difference between is the specific value of independent variable. Thus, effects of the experimental treatment are evaluated. A control group ensures consistence of stimulus characteristics so responses can carefully measured (Martin, 1996). For example, a group of phobic patients is treated and found to be less fearful after than before treatment. Yet, no evidence can prove the treatment is responsible for the change. By adopting a control group and compare it with the experimental group, a conclusion can be made as the change is due to the treatment (Liebert, 1995). The data collected is then valid. However, there is experimenter bias when experimenter pays more attention to either of the 2 groups. This will unintentionally influence the result (Mcguigan, 1993). To avoid, double-blind procedure is executed. Double-blind procedure is neither participants nor experimenters are aware of what level of the independent variable the participant is exposed to (Myer, 2000).
A new drug study can demonstrate how control group, together with double-blind procedure enhance experimental accuracy. A placebo is presented to control group in this experiment. Giving a placebo produces an effect of ingestion of a therapeutic substance (Liebert, 1995). As the placebo has no real healing power on the control group, the experimenters can deduce whether the new drug is efficient.
The basic elements of an experiment are the environmental conditions following the hypothesis, independent and dependent variable, application of control group and double-blind procedure. The comparison between control group and experimental group allows researcher to make causal interpretations accurately as extraneous variable is eliminated, no variables but only independent variable tested is affecting the dependent variable.
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