Endgames Statistical Question

Evaluating the performance of a screening test for depression in primary care

BMJ 2015; 350 doi: https://doi.org/10.1136/bmj.h1801 (Published 09 April 2015) Cite this as: BMJ 2015;350:h1801
  1. Philip Sedgwick, reader in medical statistics and medical education,
  2. Katherine Joekes, senior lecturer in clinical communication
  1. 1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}sgul.ac.uk

The accuracy of asking patients two questions as a screening test for depression in primary care was evaluated. The first question focused on depressed mood: “During the past month have you often been bothered by feeling down, depressed, or hopeless?” The second focused on pleasure: “During the past month have you often been bothered by little interest or pleasure in doing things?” A cross sectional study was performed. In total, 670 consecutive patients attending their general practice who were not taking psychotropic drugs were invited to participate, of whom 421 agreed. Patients were asked the two questions at any time during their consultation, and if the response to either was yes, screening was considered “positive” and the patient deemed at “high risk” of depression; otherwise screening was considered “negative” and the patient was deemed at “low risk” of depression. A self completed, computerised, international diagnostic interview was used to diagnose depression.1

Overall, 29 of the 421 patients (6.9%) were diagnosed as having depression. The two questions had a sensitivity of 96.6%, specificity of 67.1%, positive predictive value of 17.8%, and negative predictive value of 99.6% as a screening test for depression.

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

  • a) Only patients with a positive screening test result underwent the diagnostic interview

  • b) A “true positive” was a patient with a “positive” screening test result who was subsequently diagnosed as having depression at the diagnostic interview

  • c) The sensitivity of the screening test was the proportion of patients diagnosed as having depression who were identified as “positive” at screening

  • d) The positive predictive value was the proportion of patients with a positive (high risk) result subsequently diagnosed as having depression at the interview

Answers

Statements b, c, and d are true, whereas a is false.

It is …

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