hazelnut wrote:
For a university study on exercise habits, three equal groups were each led in one type of exercise for 45 minutes each day for a month: rowing, jogging, and dancing. When surveyed three months later, about half of those in the jogging and rowing groups were still participating in that activity at least twice per week, but for the dance group that figure was closer to 80%. It can be concluded, then, that of the three types of exercise dance is the activity that people are most likely to continue pursuing once they’ve started.
Which of the following is an assumption upon which the argument relies?
(A) Of the survey participants who changed to a different type of exercise after the survey ended, fewer changed from dance to another activity than changed from either jogging or rowing to dance.
(B) Joggers and rowers are no more likely than dancers to become injured while pursuing their chosen activity.
(C) Dance is an activity for which participants are less dependent on favorable weather than jogging and rowing are.
(D) The ratio of study participants who chose their activity to those who were randomly assigned their activity was no lower for jogging and rowing than it was for dancing.
(E) The number of participants in the dance group was no lower than the number of participants in the jogging and rowing groups.
VERITAS PREP OFFICIAL EXPLANATION:
A common logical flaw with regard to statistics is that of correlation vs. causation: here the argument wants us to be impressed by the comparison between 80% and "about half," but do we know that 80% retention rate for dance reflects improvement from before the study, or was the group of dancers always more likely to stick with dancing?
With assumption questions, you can often get a better feel for the flaw in logic, and necessity of the right answer to plug that flaw, if you use the Assumption Negation Technique, essentially turning the Assumption question into a Weaken question by taking the opposite of each answer and determining whether that rephrased choice directly weakens the argument.
With choice D, you should see that if the opposite were true - if the ratio of people who picked their activity to people who were assigned it was higher for dancers than for the other groups - then you don't know whether that rate of retention (a higher percentage kept dancing) was because dancing is inherently an easier activity for anyone to stick with, or because this particular group was already predisposed to want to keep dancing. Essentially, without answer choice D, you don't know whether you have a valid control group to effectively compare activity to activity.
Of the incorrect answer choices, choice B is often the most tempting for people. But keep in mind that the conclusion is only concerned with whether people continue to pursue the activity, not with why they might not be able to pursue it. If joggers and rowers were more likely to become injured (the negated choice B), that only supports the conclusion that people are more likely to continue with dance - not necessarily because they prefer it, but because they cannot keep up with the other activities. Since B and C, each negated, go on to support the conclusion, they are incorrect.