Transportability of Outcome Measurement Error Correction: from Validation Studies to Intervention Trials

Many lifestyle intervention trials depend on collecting self-reported outcomes, like dietary intake, to assess the intervention's effectiveness. Self-reported outcome measures are subject to measurement error, which could impact treatment effect estimation. External validation studies measure both self-reported outcomes and an accompanying biomarker, and can therefore be used for measurement error correction. Most validation data, though, are only relevant for outcomes under control conditions. Statistical methods have been developed to use external validation data to correct for outcome measurement error under control, and then conduct sensitivity analyses around the error under treatment to obtain estimates of the corrected average treatment effect. However, an assumption underlying this approach is that the measurement error structure of the outcome is the same in both the validation sample and the intervention trial, so that the error correction is transportable to the trial. This may not always be a valid assumption to make. In this paper, we propose an approach that adjusts the validation sample to better resemble the trial sample and thus leads to more transportable measurement error corrections. We also formally investigate when bias due to poor transportability may arise. Lastly, we examine the method performance using simulation, and illustrate them using PREMIER, a multi-arm lifestyle intervention trial measuring self-reported sodium intake as an outcome, and OPEN, a validation study that measures both self-reported diet and urinary biomarkers.