We used three indicators (or proxy measures) to identify persons with depressive symptoms. First, participants responded to the self-administered 30-item General Health Questionnaire (GHQ) at phases 3, 5, 7, and 9, a screening instrument designed for and widely used in population-based surveys and trials (26). Each questionnaire item enquires about a specific symptom, with response categories scored as either 1 or 0 to indicate whether the symptom is present. Total score of 5 or more led to individuals being defined as GHQ-symptom cases and scores 0 to 4 as noncases (27). Although the GHQ was originally designed to assess depressive and anxiety symptoms, a recent population-based study showed GHQ caseness to be sensitive (84%) and specific (84%) in detecting dysthymia or major depressive disorder, as indicated by the Composite International Diagnostic Interview (28). The GHQ has also been validated at baseline against a clinical interview schedule in the Whitehall II study, with acceptable sensitivity (73%) and specificity (78%) (27). In a more recent validation using a subgroup of 274 participants aged 58 to 70 in 2010, the sensitivity and specificity of GHQ symptom caseness against diagnosed depressive episodes based on a structured psychiatric interview were 80% and 81%, respectively.
indicators (or proxy measures)
three
General Health Questionnaire (GHQ)
30-item
item
response categories
scored
1 or 0
GHQ-symptom cases
score
5 or more
noncases
scores
0 to 4
GHQ caseness
sensitive
84%
%
GHQ caseness
specific
84%
%
GHQ
sensitivity
73%
%
GHQ
specificity
78%
%
subgroup
274 participants
participants
subgroup of 274 participants
aged
58 to 70
more recent validation
2010
GHQ symptom caseness
sensitivity
80%
%
GHQ symptom caseness
specificity
81%
%