Reliability and validity of a modified PHQ-9 item inventory (PHQ-12) as a screening instrument for assessing depression in Asian Indians (CURES-65).
OBJECTIVES
To evaluate the validity and reliability of the modified Patient Health Questionnaire(PHQ) 12 item instrument as a screening tool for assessing depression compared to the PHQ-9 in a representative south Indian urban population.


METHODS
The Chennai Urban Rural Epidemiology Study [CURES] is a large cross-sectional study conducted in Chennai, South India. In Phase 1 of CURES(urban component), 26,001 individuals aged > or =20 years individuals were selected by a systematic sampling technique of whom one hundred subjects were randomly selected, using computer-generated numbers, for this validation study. Two self-reported questionnaires (modified PHQ-12 item and PHQ-9 item) were administered to the subjects to compare their effectiveness in detecting depression. Reliability and validity were assessed and Receiver Operating Characteristic (ROC) curves were plotted. Pearson's correlation was used to compare the two questionnaires.


RESULTS
The mean age of the study was 38.6 +/- 11.6 years and 48% were males. Pearson's correlation coefficient between the modified PHQ-12 and the PHQ-9 item was 0.913 [p < 0.0001]. Factor Analysis revealed that the modified PHQ-12 item scale can be used as a unidimensional scale and had excellent internal consistency (Cronbach's alpha: 0.88). A cut point of >4 calculated using the ROC curves for the modified PHQ-12 item had the highest sensitivity (92.0%) and specificity (90.7%) using PHQ-9 as the gold standard. The positive predictive value was 76.7%, and the negative predictive value, 97.1% and the area under the ROC curve, 0.979 (95% Confidence Interval: 0.929 - 0.997, p < 0.0001).


CONCLUSION
The modified PHQ-12 item is a valid and reliable instrument for large scale population based screening of depression in Asian Indians and a cut point score of greater than 4 gave the highest sensitivity and specificity.