In each of the following cases, tell whether it would be best to examine the independent variable in a within-subjects or a between-subjects design. Justify your answer in each case.
a. A social psychological study of helping, in which the researchers are interested in how group size affects whether or not an individual will help someone else in the group.
b. A study of the effect of varying loudness of a tone in measuring how quickly people can respond to the tone.
c. An experiment designed to answer the question of whether the color of a woman’s hair affects the likelihood that she will be asked out for dates.
d. A study in which three different training techniques are compared as to their effectiveness in teaching animals tricks.