Risk of bias from inclusion of patients who already have diagnosis of or are undergoing treatment for depression in diagnostic accuracy studies of screening tools for depression: systematic reviewBMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d4825 (Published 18 August 2011) Cite this as: BMJ 2011;343:d4825
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Thombs and associates recently demonstrated that the sensitivity and
predictive value of depression screening tools have been artificially
inflated by the inclusion of known cases depression in the screened
populations . However, there is an additional and potentially serious
problem with screening in mental health that is not evident in other forms
of health screening.
In mental health screening a useful sensitivity is
achieved by questionnaires including items that are very similar to
diagnostic items. For example, the General Health Questionnaire - 12 (GHQ
-12) includes questions about impaired concentration, insomnia, and
feelings of worthlessness and feelings of depression . These items are
also present in the recognised diagnostic criteria for depression [3 4].
Patients who are thought to be at high risk of depression because of a
high GHQ - 12 score are more likely to have these complaints. Thus the
presence of these symptoms in many patients reduces their diagnostic
discriminability in populations of people who have previously screened
positive on a GHQ -12. Put bluntly in a population of people who report
insomnia, insomnia is of no value in determining who is and who is not
depressed. Similar issues also arise in screening for violence risk 
where factors such as young age, male sex and substance use might be used
in a screening test and to assess more definitively the potential for
future violence. The World Health Organisation suggests that health
screening should be followed by a specific diagnostic test . Any
reconsideration of the role of screening in mental health should consider
both the role of known cases when estimating the sensitivity of the
screening test and the potential for screening to reduce the specificity
of the diagnostic interview.
1. Thombs BD, Arthurs E, El-Baalbaki G, Meijer A, Ziegelstein RC,
Steele RJ. Risk of bias from inclusion of patients who already have
diagnosis of or are undergoing treatment for depression in diagnostic
accuracy studies of screening tools for depression: systematic review. BMJ
2. Goldberg DP, Williams PA. User's Guide to the General Health
Questionnaire. NFER-NELSON 1988.
3. American Psychiatric Association. Diagnostic and Statistical
Manual, 4th edition, text revision (DSM-IV-TR. American Psychiatric Press
4. Organisation WH. International Classification of Diseases -
Version 10. Accessed from http://www.who.int/classifications/icd/en/ 22
May 2011 1990.
5. Roaldset JO, Hartvig P, Bjorkly S. V-RISK-10: validation of a
screen for risk of violence after discharge from acute psychiatry. Eur
6. Wilson JMG, ., Jungner G. Principles and practice of screening for
disease. Geneva: WHO 1968;accessed from
http://whqlibdoc.who.int/php/WHO_PHP_34.pdf 25th August 2011.
Competing interests: No competing interests