Shortening the PHQ-9: a proof-of-principle study of utilizing Stochastic Curtailment as a method for constructing ultrashort screening instruments.

OBJECTIVE

In primary care, screening instruments for mental health should be ultrashort to allow for routine usage. In this paper, Stochastic Curtailment is introduced as a method for constructing ultrashort screeners.

METHOD

In a post hoc diagnostic accuracy study using the item scores on the Patient Health Questionnaire depression module (PHQ-9) of a large sample (N=20, 685), Stochastic Curtailment was compared with two existing ultrashort versions of PHQ-9. The first was PHQ-2 (which includes the first two items of PHQ-9), and the second was a 'two-step' method (only if the PHQ-2 screened positive were all nine PHQ items administered). For PHQ-2 and two-step, both cut scores 2 and 3 were evaluated.

RESULTS

PHQ-2 showed the lowest and Stochastic Curtailment the highest diagnostic accuracy with reference to the classifications based on the full PHQ-9. To do so, Stochastic Curtailment used 3.08 items on average (S.D.=1.98), which was slightly less than two-step (M=3.18, S.D.=2.62) under its most accurate cut score (≥2).

CONCLUSIONS

It was concluded that Stochastic Curtailment is a promising method for constructing ultrashort screeners.