... 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. ...

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