Confoundings and Internal Validity

1			An investigator develops the idea that an excess of a particular chemical (RTQX) in the brain during infancy produces permanent mental retardation. To gather evidence for this notion, he uses 30 infant rats and their mothers in an experiment. The rats (infant and mother) are assigned to two groups of 15 infant-mother combinations on a random basis. In the C Group, the infant rats are nursed by the mother rats. In the E Group, infant rats are kept separated from their mothers and fed by bottle. The chemical RTQX is mixed with the milk in the nursing bottle. Tests of mental development are made on both groups at various points in time, even far beyond the nursing period. At every point of the testing, the infant rats in the E Group are found to be inferior to those in the C Group. The experimenter concludes that the chemical RTQX causes mental retardation. Do you agree?
2			A group of researchers sought to develop a program to help students cope with adjustment to college during the first year of college. Students were randomly assigned to participate in one of two groups, the control group or the experimental group. Students in the control group participated in the fall term. The researchers assessed these students' experience of stress, anxiety, and depression at the end of the fall term. No "treatment" was given to these students, so that the researchers would have a measure of students' naturally-occurring adjustment reactions to college. The experimental group participated during the spring term. In addition to assessing their experience of stress, anxiety, and depression at the end of the spring term, these students participated in a series of stress-reduction workshops during the spring term. The results of this study indicated that students who participated in the experimental stress-reduction workshops experienced less stress, anxiety, and depression than did students in the control group. The researchers concluded that the program to help students cope with adjustment to college was successful.