Endgames Statistical Question

Measuring the performance of screening tests

BMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g4438 (Published 07 July 2014) Cite this as: BMJ 2014;348:g4438
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Institute of Medical and Biomedical Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}sgul.ac.uk

Researchers assessed the performance of the SCOFF questionnaire as a screening tool in primary care for eating disorders. The questionnaire consists of five questions related to the core features of anorexia nervosa and bulimia nervosa. The study participants were 341 consecutive female attendees aged 18-50 years at two general practices. All women completed the SCOFF questionnaire and underwent a clinical diagnostic interview. If a woman responded “yes” to two or more of the five questions on the SCOFF questionnaire she was identified as “positive” and at “high risk” of eating disorders; otherwise she was identified as “negative” and at “low risk” of eating disorders. A diagnosis of eating disorders was confirmed through a clinical diagnostic interview for eating disorders based on criteria from the Diagnostic and Statistical Manual of Mental Disorders (fourth edition).1

The SCOFF questionnaire had a sensitivity of 84.6%, specificity of 89.6%, positive predictive value of 24.4%, and negative predictive value of 99.3%.

Which of the following statements, if any, are true?

  • a) The sensitivity is the proportion of women with a diagnosed eating disorder identified as positive on screening

  • b) The specificity is the proportion of women without a diagnosed eating disorder identified as negative on screening

  • c) The positive predictive value is the proportion of women with a positive result on screening who had a diagnosed eating disorder

  • d) The negative predictive value is the proportion of women with a negative result on screening who were found not to have a diagnosed eating disorder

Answers

Statements a, b, c, and d are all true.

It would be impractical for all women in primary care to have a clinical diagnostic interview for eating disorders. Not only would this be time consuming and expensive, but it would probably be inconvenient and unnecessary for most women. …

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