Optimal Cut-Off Points for the Short-Negative Act Questionnaire and Their Association with Depressive Symptoms and Diagnosis of Depression.

Objectives: The behavioural experience method has been extensively used in the literature for the measurement of potential bullying behaviours at work. However, this approach presents limitations when used to classify respondents as targets or non-targets of workplace bullying. Therefore, the present study aimed to: (i) identify optimal cut-off points, reflecting a possible subjectively experienced exposure to occasional and frequent workplace bullying, for the 9-item Short Negative Act Questionnaire (S-NAQ), and (ii) examine the criterion validity of these cut-off points in relation to depressive symptoms and diagnosis of depression.

Methods: The study was based on a sample of 4882 participants from the Danish MODENA cohort study (year 2011), which included both the S-NAQ (score range 9-45) and a one-item measure applying the self-labelling method with a definition to assess occasional and frequent workplace bullying. We employed receiver operating characteristic (ROC) curve analyses to derive the cut-off points for the S-NAQ. Based on these cut-off points, we created a new S-NAQ variable with three levels of exposure (i.e. 'not exposed', 'first threshold', and 'second threshold') and tested its criterion validity in relation to depressive symptoms (N = 4071) and diagnosis of depression (N = 4844).

Results: The S-NAQ cut-off points obtained were ≥12 and ≥16 when using occasional and frequent bullying as reference standards, respectively. Both cut-off points showed high classification accuracy (area under the curve = 0.89 and 0.93) as well as good sensitivity (84.8% and 88.0%) and specificity (77.4% and 94.7%). In the adjusted linear regression analyses, both the first (B = 0.78, 95% confidence interval [CI] = 0.66-0.90) and the second threshold of exposure (B = 1.65, 95% CI = 1.44-1.86) were significantly associated with depressive symptoms. In the adjusted logistic regression analyses, both the first (odds ratio [OR] = 3.55, 95% CI = 1.98-6.38) and the second threshold of exposure (OR = 5.90, 95% CI = 2.93-11.88) were significantly associated with diagnosis of depression.

Conclusions: The two cut-off points for the S-NAQ identified in this study showed a significant association with both depressive symptoms and diagnosis of depression. However, future prospective studies are needed to establish the predictive validity of the proposed cut-off points.