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.

Keywords:
Screening; Mental health; Respondent burden; Curtailment