Random assignment of subjects to experimental and control groups has which of these effects?
a. Minimizes mortality within groups
b. Maximizes variance between groups
c. Decreases systematic bias
d. Increases selection bias
ANS: C
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A Randomization has no effect on mortality (dropout rate).
B Randomization minimizes pretreatment variance between groups, rather than maximizing variance. This helps to ensure that posttreatment differences are related to the independent (treatment) variable alone.
C Random assignment to groups helps to ensure that other (extraneous) variables that could affect changes in the dependent variable are equally distributed within groups, thus reducing systematic bias.
D Randomization reduces selection bias, rather than increasing it.
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