We felt that a measure specifically validated to screen for depressive symptoms in adolescents in India was required. This study was the first one to evaluate the psychometric properties of BDI in India among adolescents and demonstrates the validity as well as diagnostic accuracy of BDI as a screening measure among adolescents attending school while used by paediatricians. These findings build upon previously published validation data, which has demonstrated the use of BDI in many setting and culture [12, 13, 20–22].
The diagnostic accuracy parameters of sensitivity and specificity were achieved for screening and diagnostic purpose in our study. For the screening procedures a threshold score of ≤ 5 yielded the maximum clinical efficiency with a sensitivity and specificity of 90.9% and 17.6% respectively. Where as for a diagnostic use a threshold score of ≥ 22 provided a sensitivity and specificity of 27.3% and 90.0% respectively, which are comparable with previous study among adults  and adolescents  in primary-care settings. Like the past studies, we also have recommended two cut-off scores instead of score ranges to classify the severity of depression as was originally used [11, 12] as we have validated BDI as screening or diagnostic measure of depressive syndromes,
Among the different parameters used to assess the reproducibility, the inter-rater reliability is not appropriate for the BDI as it is a self-rated measure  and therefore only test-retest reliability was done in this study. The test-retest reliability was found to be good and is comparable with that of the test-retest reliability of 0.48 to 0.86 reported at 2 to 6 weeks .
The face and content validity of BDI as a measure for depression has long been established by consensus among clinicians  and it has been shown that the BDI items are consistent with six of the nine Diagnostic and Statistical Manual, Edition III (DSM-III) categories of symptom clusters of depression . The content validity of BDI in this study was as good as reported elsewhere .
The method of Cronbach's alpha was applied to evaluate the scale item homogeneity. The internal consistency of BDI in our study was high and in agreement with what has been reported in other studies. Among the previous studies, the internal consistency for the BDI has ranged from .73 to .92 with a mean of .86 [10, 25].
The convergent validity of the BDI has not been documented in the adolescent population with other psychometrically sound instruments for depression. However, the convergent validity of BDI with Hamilton Psychiatric Rating Scale for Depression has been (0.73), Zung Self Reported Depression Scale (0.76) and the MMPI Depression Scale (0.76) among adults . In the present study the convergent validity between the BDI and the Children's Depression Rating Scale had been high among the adolescents. The BDI mean score was relatively high with where as the prevalence of clinically diagnosed depression was low and this could have happened because it is known that high BDI scores in the absence of clinical depression can occur when there are non-depressive symptoms like anxiety symptoms . Depressive symptoms among our adolescents could also have occurred because of the developmental stage related environmental issues shaming, self-verification, self efficacy, attachment insecurity, maladaptive coping and attribution styles or environmental factors like parenting issues .
The discriminant validity of the BDI in our study was high demonstrating that it can differentiate other psychiatric disorders like Post-traumatic Stress Disorder that can have affective symptoms. On the other hand, as the co-morbidity overlap of PTSD and depression is common, using IES as the discriminant measure could have compromised the discriminant validity from having even higher values. Many past studies have found that the BDI discriminates depressive symptoms from depressive disorder, dysthymic disorders, loneliness, stress and non-psychiatric patients among adults [25, 28–32]. Recently, the ability of the BDI to discriminate adolescents with depression from those who are not depressed has also been established .
This study demonstrated a two-factor model for BDI. Previous data on the construct validity of BDI has documented two to seven factors, depending on the method of factor extraction . Both the factors, Factor 1 (Somatic symptoms) and Factor 2 (Mood-negative cognitions) had only 4 and 3 factors falling under them respectively and in the previous studies also it had been proposed that only a few factors and items are stable . This lack of stability of the construct over studies has been speculated because of the measurement of state and trait of depression by the BDI .
A few limitations of this study must be acknowledged. Firstly, the low prevalence of depression in the sample could have limited the power and stability of the sensitivity analyses. Further, recruiting school children with ablility to read and write English atleast at sixth grade level could have introduced some selection bias. Other shortcomings of the BDI are its controversial factorial validity, and poor discriminant validity against anxiety. Lack of a representative norm could have componded the factor structure further and not including adolescents with anxiety symptoms did not address the discriminant validity against anxiety disorders. It should be noted that BDI provides a measure of severity of depressive symptoms and further clinical assessment may be needed for confirmation of a syndrome of depression, thus BDI is not a diagnostic tool for depressive disorders. We have used the term 'diagnostic accuracy' only to be in concordance with the STARD guidelines for reporting validation studies.