Terluin, B.

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Malaysian GAD-7 less sensitive than reported

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262 VOLUME 4 • NUMBER 3 • SEPTEMBER 2012  J OURNAL OF PRIMARY HEALTH CARE
Letters may respond to published papers, briefly report original research or case reports, or raise matters of interest relevant to 
primary health care. The best letters are succinct and stimulating. Letters of no more than 400 words may be emailed to:  
editor@rnzcgp.org.nz. All letters are subject to editing and may be shortened.
LETTERS TO THE EDITOR
Malaysian GAD-7 less sensitive than reported
In their paper on the validation of the Malay version of the GAD-7, Sidik et al. reported acceptable sensitivity (76.3%) and 
excellent specificity (94.4%) for detecting anxiety disorder in 
consecutive women attending a primary care clinic.1 However, 
these results are biased because the authors failed to account 
for the stratified sampling procedure. When a stratified sam-
pling procedure has been applied, the data must be ‘weighted 
back’ to mirror the source population in order to produce 
unbiased estimates of the operating characteristics for that 
population. Sidik et al. included 895 women who completed a 
PHQ-9 and GAD-7. Then they divided the group into women 
with normal scores (PHQ-9 <10 and GAD-7 <5) and women 
with high scores (PHQ-9 ≥10 and GAD-7 ≥5). From the first 
group, one in 10 women and from the second group one in two 
women were selected for a psychiatric diagnostic interview. 
Fifty participants were excluded, leaving 845 overall partici-
pants of whom 146 underwent a diagnostic interview. Sidik 
et al.’s Table 1 informs us that 38 of the latter 146 women had 
an anxiety disorder diagnosis and 35 of the 146 women had a 
positive GAD-7 test (≥8). In addition, Sidik et al. provided the 
information that 66 of the original 845 women (i.e. 7.8%) had a 
positive GAD-7 test. We can use this information to try to cal-
culate the expected numbers for Table 1 when all 845 women 
(representing the source population of women attending the 
clinic) would have been examined instead of the stratified 
sample of 146: From a total of 845 women, 66 had a positive 
and 779 a negative GAD-7. Thus, the 35 women with a positive 
GAD-7 (from the 146 women examined) represented a sample 
of the original 66 women with a positive GAD-7. To weight 
back these women to the source population, they are assigned 
a weight factor of 66/35=1.9. The 29 women with a positive 
GAD-7 and an anxiety disorder diagnosis therefore probably 
represented 29 x 1.9 = 55 women in the source population. 
Similarly, the six women with a positive GAD-7 and no anxi-
ety disorder diagnosis probably represented 6 x 1.9 = 11 women 
in the source population. Analogously, the weight factor for 
women with a negative GAD-7 is 779/111 = 7.0. The nine 
women with a negative GAD-7 and an anxiety disorder diag-
nosis probably represented 9 x 7.0 = 63 women in the source 
population (!). A complete redraw of Table 1 looks like this:
Table 1. Numbers weighted back to mirror the source population
Anxiety 
diagnosis
No anxiety 
diagnosis
Total
GAD-7 positive 55 11 66
GAD-7 negative 63 716 779
Total 118 727 845
Sensitivity of the GAD-7 in the source population was 55/118 
= 46.6% (instead of 76.3% in the stratified sample). Specificity 
was 98.5%, the LR of a positive test was 30.81 and the LR of a 
negative test was 0.54%. The revised conclusion should be that 
the GAD-7 did not perform very well in detecting anxiety dis-
order in the Malaysian women attending a primary care clinic: 
the GAD-7 missed more than half of all anxiety disorders.
Berend Terluin, MD, PhD
Dpt. of General Practice and Elderly Care Medicine, 
EMGO Institute for Health and Care Research, 
VU University Medical Centre, Amsterdam, Netherlands
Authors’ response
In response to the ‘Letter to the Editor’ on the validity results of the GAD-7 (Malay version), the authors would like to maintain that their original cal-
culations are correct. The validity of the GAD-7 (Malay version) was calculated based on the 146 participants interviewed with the CIDI, and not the 
whole study population (n=845). The objective of the paper was to validate the GAD-7 against the CIDI as the reference standard, which was stated 
in the abstract and method sections. Therefore, the authors are justified in calculating the sensitivity and specificity of the GAD-7 only among the 
146 participants who were interviewed with the CIDI. The remaining 699 respondents were not interviewed with the CIDI, and therefore the validity 
findings were not generalised to the whole study population of 845. The sensitivity and specificity of a test are independent of the prevalence of a 
disorder. We accept that the likelihood ratios are based on small numbers but they are also independent of prevalence. Dr Terluin’s extrapolation of 
results from a subset onto the total population, including those who had not had the reference standard risks, must be interpreted with caution due to 
the potential magnification of error, where numbers in some groups are actually small.
Reference
1. Sidik S, Arroll B, Goodyear-Smith F. Validation of the GAD-7 (Malay version) 
among women attending a primary care clinic in Malaysia. J Prim Health Care. 
2012;4(1):5–11.


Malaysian GAD-7 less sensitive than reported

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