True/False Items

The Advantages and Disadvantages of True/False Questions

The advantages of multiple-choice items are considerable. First, they are convenient, such that several can be administered in a short amount of time. Second, they are very easy to score. If well written, the answers are either correct or incorrect.

But, as with all items, there are disadvantages as well. First, true/false items place a premium on memorization. It is tough to get beyond the most basic levels of knowledge with true/false items. Second, it is relatively easy to guess correctly; the probability of being right (or wrong) is 50%, and by chance alone, if the test taker selects T or F on a somewhat random [Page 1014]basis, the final score will be about 50%. Still, the odds of guessing correctly are much higher than in any other type of traditional item.

True/false test scores can be corrected for guessing (that is the chance outcome of getting 50% correct by guessing alone). This is a useful adjustment to make so that scores more truly reflect those who really do know more versus those who just guess.

Let's propose a scoring system where students get one point for being correct, one point for being incorrect, and nothing for leaving the item blank. So, the formula for correction (or CS, for corrected score) becomes

For example, take the example of a 50-item test, where you would expect a score of 25 by chance alone (.5 × 50 = 25). Bruce gets 35 correct on a 50-item test, and Bill gets 25 correct. How can we adjust these scores so that Bruce's performance (which is way above chance) is recognized?

Correcting the scores, it turns out that Bruce's new one is 35 − 15 = 20, and Bill's is 25 − 25 = 0. Bill is clearly “punished” for guessing.

Table 1 Corrected Scores on 50-Item Test
# Right	# Wrong	Corrected Score
50	0	50
45	5	40
40	10	30
35	15	20
30	20	10
25 (chance)	25 (chance)	0
20	30	–10
15	35	–20
10	40	–30
5	45	–40
0	50	–50

Table 1 shows the number correct on a 50-item test, the number wrong, and the corrected score.

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