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Abstract
Objective
Some medications require specific medical procedures in the weeks before their start.
Such procedures may meet the definition of instrumental variables (IVs). We examined
how they may influence treatment effect estimation in propensity score (PS)-adjusted
comparative studies, and how to remedy.
Study Design and Setting
Different covariate assessment periods (CAP) did and did not include the month preceding
treatment start were used to compute PS in the French claims database (SNDS), and
1:1 match patients with metastatic castration resistant prostate cancer initiating
abiraterone acetate or docetaxel. The 36-month survival was assessed.
Results
Among 1 213 docetaxel and 2 442 abiraterone initiators, the PS distribution resulting
from the CAP [-12; 0 months] distinctly separated populations (c=0.93; 273 matched-pairs).
The CAP [-12;-1 months] identified 765 pairs (c=0.81). Strong docetaxel treatment
predictors during the month before treatment start were implantable delivery systems
(1% vs. 59%), which fulfilled IV conditions. The 36-month survival was not meaningfully
different under the [-12;0 months] CAP but differed by 10% points (38% vs. 28%) after
excluding month -1.
Conclusion
In setting of highly predictive pre-treatment procedures, excluding the immediate
pre-exposure time from the CAP will reduce the risk of including potential IVs in
PS models and may reduce bias.
Keywords
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Article info
Publication history
Accepted:
January 11,
2023
Received in revised form:
December 10,
2022
Received:
September 16,
2022
Publication stage
In Press Journal Pre-ProofIdentification
Copyright
© 2023 Elsevier Inc. All rights reserved.
