Why should negatively worded stems be avoided in MCQs?
Negatively worded stems ("Which is NOT…", "All EXCEPT…") add reading burden without testing more knowledge, are easily misread by hurried or non-native examinees, and reward test-taking care over content mastery. Haladyna, Downing and Rodriguez (2002) recommend wording stems positively; if a negative is unavoidable, emphasize it with capitals or bold.
A negatively worded stem asks the examinee to find the exception: "Which of the following is NOT a feature of nephrotic syndrome?" or "All of the following are appropriate EXCEPT…". These items are popular with writers because they are easy to produce — list three true things and one false one — but the measurement literature consistently recommends against them.
The problems
They are easy to misread. Under time pressure, examinees skim stems, and a single "not" or "except" is exactly the kind of word skimming misses. An examinee who knows the content perfectly can miss the item by reading past the negative — and an item that punishes reading lapses rather than knowledge gaps is measuring the wrong construct. The burden falls hardest on non-native English speakers and anxious test-takers, which raises fairness concerns on high-stakes exams.
They impose extra cognitive load without testing more. Answering a negative item requires evaluating each option as true or false and then inverting the selection logic. That extra processing tests working memory and verbal reasoning, not the medical content the item was blueprinted to cover.
They tend to test trivia. Case and Swanson's NBME item-writing guide notes that negative items usually reduce to recognizing isolated false facts, and they resist the vignette format: it's hard to write a clinical scenario whose answer is a non-indication or a non-feature. Positively worded items ("Which of the following is the most likely diagnosis?") align naturally with clinical reasoning.
The evidence-based guidelines say so. Haladyna, Downing and Rodriguez (2002), reviewing the item-writing research, include "word the stem positively; avoid negative phrasing such as not or except" among their validated guidelines. Negative stems are also one of the flaws most frequently found in audits of faculty-written exams — Tarrant, Knierim, Hayes and Ware (2006) identified them among the recurring flaws in the nursing exams they reviewed, where roughly 46% of items had at least one writing flaw.
What to do instead
Most negative items can be rewritten positively by flipping the question. "All of the following are causes of hyperkalemia EXCEPT" becomes "Which of the following is a cause of hypokalemia?" — or better, a vignette asking for the most likely cause in a specific patient. If the learning objective genuinely concerns a contraindication or exclusion, the negative may be justified; in that case, emphasize the negative word visually (NOT, except) and never stack a negative stem on negative options ("Which is NOT an inappropriate…").
Negative wording is one item on a longer checklist — see the most common MCQ item-writing flaws for the rest, and how to write flaw-free MCQs for rewriting techniques with examples.