Difficulties in calculating productivity costs: work disability associated with borderline personality disorder

In trial-based analyses, the Human Capital (HC) approach is currently applied alternately with and without the incorporation of productivity costs for persons who are work disabled at baseline of the trial. We call these methods HC-extended (HC(EXT)) and HC-limited (HC(LIM)), respectively. Aim of the paper is to compare productivity costs according to HC(EXT) with HC(LIM) and the Friction Cost (FC) method, in patients with Borderline Personality Disorder (BPD).

Data were obtained from a multicenter randomized trial in The Netherlands, comparing two types of outpatient psychotherapy, Schema Focused Therapy (SFT, n = 44) versus Transference Focused Psychotherapy (TFP, n = 42) for BPD. Mean age was 31.7 for SFT and 29.5 for TFP. A cost-interview was administered every three months for three years, and once again after the fourth year. Productivity costs were calculated according to HC(LIM), HC(EXT) and FC. A nonparametric bootstrap resampling method was performed.

During the trial, the number of work-disabled patients increased for both treatments. Total productivity costs for HC(EXT) were higher than for HC(LIM) and FC. In addition, the incremental bootstrapped costs (TFP - SFT) pointed in the same direction for HC(LIM) (1168 Euro; 95% UI 4700 Euro, 7563 Euro) and FC (1206 Euro; -2835 Euro, 4844 Euro), but turned around for HC(EXT)(minus 1240 Euro; -9973 Euro, 7911 Euro). None of the increments were statistically significantly different from zero.

The classical and frequently discussed contrast between HC and FC is not the only difference when it concerns productivity costs. Whether or not including productivity costs for patients who are work-disabled at baseline can lead to contradictory conclusions.