Critics of sales seminars run by outside consultants point out that si

We have two groups: vacuum cleaner salesmen who attend sales seminars and those who don’t. The latter group is said to sell more. The argument concludes that sales seminars are a waste of time.

But what if the two groups vary in a significant way, making comparisons between them invalid (at least as it pertains to efficacy of sales conferences)?

Thus we want to find an answer that shows that two groups of different.


Only (A) does so by pointing out that vacuum cleaner salesmen who did not attend conferences were already selling the most vacuum cleaners. To say that they were still selling the most after the post-conferences doesn’t mean that the conferences were a “waste of money.”

Let’s use some numbers to illustrate:

Pre-1987 sales Post 1987 sales
Not-Attending V. Salesmen 10 million/person 12 million/person

Attending V. Salesmen 1 million/person 2 million/person


This shows us that the seminars can be very helpful, even when those who attended had far less in revenue than those who did not attend.

Therefore (A) is the best answer.