How to deal with cost differences at baseline.

Abstract

BACKGROUND:

To our knowledge, adjustment for baseline imbalances in costs has never been performed in trial-based cost-effectiveness analyses.

METHODS:

We used data from a clinical trial performed in the Netherlands comparing two outpatient psychotherapies: schema-focused therapy (SFT) versus transference-focused psychotherapy (TFP). Costs were assessed with a cost interview. Outcome was the proportion of recovered patients measured with the Borderline Personality Disorder Severity Index (BPDSI-IV). We used three methods to adjust the costs for baseline differences: (i) mean difference adjustment, calculating total costs after baseline by adjusting the difference between groups with the difference of the mean baseline costs; (ii) delta adjustment, calculating the individual differences between patient baseline and the subsequent measurements (concerning incremental costs, this is the same as mean difference adjustment); and (iii) regression-based adjustment, adjusting total costs with a regression model, with total costs as the dependent variable and baseline costs as the independent variable.

RESULTS:

Mean baseline costs were 3339 euros for SFT and 4238 euros for TFP, a mean difference of 899 euros. Total unadjusted follow-up costs were 30822 euros for SFT and 36812 euros for TFP. The fraction of recovered patients was 45% for SFT and 24% for TFP. Cost-effectiveness acceptability curves show that mean difference and delta adjustments are different from the regression-based methods.

CONCLUSIONS:

Although the routine starting point of an analysis should always be an unadjusted analysis of the cost effectiveness, a baseline difference between treatment groups should be adjusted for. This should be done by reported patient characteristics or, when these are not sufficiently present, by baseline costs as a substitute. This adjustment should be carried out most preferably with a regression-based method.

• Authors: Antoinette D I van Asselt, Ghislaine A P G van Mastrigt, Carmen D Dirksen, Arnoud Arntz, Johan L Severens, Alfons G H Kessels
• Journal: PharmacoEconomics (Pharmacoeconomics) Vol. 27 Issue 6 Pg. 519-28 ( 2009) ISSN: 1170-7690 [Print] New Zealand
• PMID: 19640014 (Publication Type: Journal Article)

Topics

• Borderline Personality Disorder (economics, therapy)
• Cost of Illness
• Cost-Benefit Analysis (methods)
• Humans
• Models, Economic
• Psychotherapy (economics)
• Randomized Controlled Trials as Topic