The “2 out of 5” Rule
Faculty who is setting up the paper is paid to make the question and its solution but not paid enough to make 4 other wrong options in a multiple choice question paper. In this post we are going to exploit this weakness of the MCQ questions.
It is significantly harder to create a good but incorrect answer-choice than it is to produce the correct answer. For this reason usually only two attractive answer-choices are offered. One correct; the other either intentionally misleading or only partially correct. The other three answer-choices are usually fluff. This makes educated guessing on the MCQ based questions immensely effective. If you can dismiss the three fluff choices, your probability of answering the question successfully will increase from 20% to 50%.
Example: “2 out of 5” rule
During the late seventies when Japan was rapidly expanding its share of the American auto market, GM surveyed owners of GM cars and asked, “Would you be more willing to buy a large, powerful car or a small, economical car?” Seventy percent of those who responded said that they would prefer a large car. On the basis of this survey, GM decided to continue building large cars. Yet during the ‘80s, GM lost even more of the market to the Japanese.
Which one of the following, if it were determined to be true, would best explain this discrepancy?
(A) Only 10 percent of those who were polled replied.
(B) Ford which conducted a similar survey with similar results continued to build large cars and also lost more of their market to the Japanese.
(C) The surveyed owners who preferred big cars also preferred big homes.
(D) GM determined that it would be more profitable to make big cars.
(E) Eighty percent of the owners who wanted big cars and only 40 percent of the owners who wanted small cars replied to the survey.
Only two answer-choices have any real merit—(A) and (E). The argument generalizes from the survey to the general car-buying population, so the reliability of the projection depends on how representative the sample is.
At first glance choice (A) seems rather good, because 10 percent does not seem large enough. However, political opinion polls typically are based on only .001 percent of the population. More importantly, we don’t know what percentage of GM car owners received the survey. Choice (E), on the other hand, points out that the survey did not represent the entire public, so it is the answer.
The other choices can be quickly dismissed. Choice (B) simply states that Ford made the same mistake that GM did. Choice (C) is irrelevant. Finally, choice (D), rather than explaining the discrepancy, would give even more reason for GM to continue making large cars.