A Validation Study of the Rank-Preserving Structural Failure Time Model: Confidence Intervals and Unique, Multiple, and Erroneous Solutions

Mario Ouwens, Ole Hauch and Stefan Franzén
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Mario Ouwens: AstraZeneca R&D, Mölndal, Sweden
Ole Hauch: Rue de Bordeaux, Saint-Gillis, Brussels, Belgium
Stefan Franzén: Registercentrum Västra Götaland, Göteborg, Sweden

Medical Decision Making, 2018, vol. 38, issue 4, 509-519

Abstract: Background. The rank-preserving structural failure time model (RPSFTM) is used for health technology assessment submissions to adjust for switching patients from reference to investigational treatment in cancer trials. It uses counterfactual survival (survival when only reference treatment would have been used) and assumes that, at randomization, the counterfactual survival distribution for the investigational and reference arms is identical. Previous validation reports have assumed that patients in the investigational treatment arm stay on therapy throughout the study period. Objectives. To evaluate the validity of the RPSFTM at various levels of crossover in situations in which patients are taken off the investigational drug in the investigational arm. Methods. The RPSFTM was applied to simulated datasets differing in percentage of patients switching, time of switching, underlying acceleration factor, and number of patients, using exponential distributions for the time on investigational and reference treatment. Results. There were multiple scenarios in which two solutions were found: one corresponding to identical counterfactual distributions, and the other to two different crossing counterfactual distributions. The same was found for the hazard ratio (HR). Unique solutions were observed only when switching patients were on investigational treatment for

Keywords: G-estimation method; hazard ratio; health technology assessment; rank-preserving structural failure time model; RPSFTM; treatment switching (search for similar items in EconPapers)
Date: 2018
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Persistent link: https://EconPapers.repec.org/RePEc:sae:medema:v:38:y:2018:i:4:p:509-519

DOI: 10.1177/0272989X18765175

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