In studies examining the effectiveness of vitamin C, researchers typically divide the subjects into two groups. One group (the experimental group) receives a vitamin C supplement, and the other (the control group) does not. Researchers observe both groups to determine whether one group has fewer or shorter colds than the other. The following discussion describes some of the pitfalls inherent in an experiment of this kind and ways to (a) avoid them. In sorting subjects into two groups, researchers must ensure that each person has an (b) equal chance of being assigned to either the experimental group or the control group. This is accomplished by randomization; that is, the subjects are chosen randomly from the same population by flipping a coin or some other method involving chance. Randomization helps to ensure that results reflect the treatment and not factors that might influence the grouping of subjects. Importantly, the two groups of people must be similar and must have the same track record with respect to colds to (c) rule out the possibility that observed differences in the rate, severity, or duration of colds might have occurred anyway. If, for example, the control group would normally catch twice as many colds as the experimental group, then the findings prove (d) nothing In experiments involving a nutrient, the diets of both groups must also be (e) different especially with respect to the nutrient being studied. If those in the experimental group were receiving less vitamin C from their usual diet, then any effects of the supplement may not be apparent.
* pitfall: 함정