The American Board of Ophthalmology writes multiple-choice examination questions (items) with four options: A, B, C, and D. One of those options is correct (the key). Why do we write four options?
This is a hotly debated topic among psychometricians. Some researchers prefer three options, some think four is best, and some advocate for as many options as are reasonable in the context of the question. The research on this topic has focused on whether distractors (incorrect options) were functioning as intended. An ideal distractor is selected by at least some examinees and exhibits negative discrimination (i.e., weaker-performing examinees are more likely than stronger-performing examinees to select an incorrect distractor). Two leading experts on this topic conducted a study where they found that if all non-functioning distractors (those distractors that attracted no or very few examinees) were removed from items, most items would end up with only two or three options. Another study found that four or five options are best if measurement precision is desired at the lower end of the ability continuum.
The ABO uses four because we have found, in most cases, that all three distractors function as intended. It is important to note that even though we look for items that discriminate among examinees, all of ABO’s tests are criterion-referenced, which means it is possible for everyone to pass or everyone to fail depending on whether or not they meet the performance standard. The performance of an individual (whether strong or weak) does not affect the score of any other individual. The ultimate goal for any item selected for use on an exam is content relevance.