Cognitive Failures Questionnaire (CFQ)
Broadbent's 25-item measure of everyday memory, attention, and action slips: the standard brain fog questionnaire
Brain fog is one of the most common complaints in long COVID and ME/CFS, and one of the hardest to put a number on. The Cognitive Failures Questionnaire, published by Donald Broadbent and colleagues at Oxford in 1982, is the most widely used self-report instrument for everyday cognitive lapses: forgetting why you walked into a room, reading a paragraph and taking nothing in, losing your thread mid-sentence. You rate how often 25 such lapses have happened over the past six months, from 0 (never) to 4 (very often), for a total of 0–100.
Healthy adults typically score in the low-to-mid 30s. Long COVID cohorts have averaged in the mid-40s to 50, and ME/CFS patients higher still. The questionnaire does not measure cognitive performance (scores correlate only modestly with objective testing), but it does capture the lived frequency of lapses, which is what most people mean by brain fog and what clinicians rarely have a number for. The results also give three subscales: forgetfulness, distractibility, and blunders.
The questionnaire is presented in two pages of 12–13 items. If mental fatigue rather than lapses is your main concern, the Chalder Fatigue Scale has a mental fatigue subscale, and the DSQ-PEM characterises symptoms that worsen after cognitive effort.
Your Cognitive Failures Questionnaire score
Subscales
Average item score (0–4) in each of the three factors identified by Rast and colleagues (2009). Not all 25 items load on a factor.
Where your total sits
Understanding your score
Reference values. Broadbent's original working samples averaged 35–37 (student nurses 52). A US community sample of 839 adults averaged 31.7 (SD 12.7); UK naval personnel averaged 37.6 (SD 14.0). Several clinical studies use 43 or more as a high score, being one standard deviation above the mean of a Dutch reference sample. There is no validated diagnostic cut-off.
Post-viral cohorts. In a 2024 UK study, people with post-COVID syndrome averaged 44.4 against 32.7 in people who had never had COVID; another 2024 study reported 50.2 versus 25.9. Danish post-COVID clinic patients averaged 61–67, with 83–90% scoring 43 or more. People with ME/CFS averaged 57.4 in a 2014 study. In the UK study, CFQ scores did not track objective test performance, which supports using the CFQ as a record of experience rather than a proxy for cognitive testing.
Subscales. Forgetfulness (items 2, 6, 16, 17, 23), distractibility (1, 3, 7, 9, 19, 21), and false triggering or blunders (5, 8, 10, 14, 15, 18, 24, 25) come from Rast and colleagues' 2009 factor analysis. Later work suggests the total score is the most reliable summary; treat the subscale profile as a description of where your lapses cluster, not as separate measures.
The six-month recall period makes the CFQ a slow-moving measure. Repeating it every three to six months, or before and after a significant change, is appropriate. If cognitive symptoms are affecting work or safety, ask your GP about referral for formal cognitive assessment.
This is not a diagnosis. Discuss your results with your doctor or specialist.