PhD: Estimating and extrapolating recruitment rates from pilot trials

University of Sheffield - School of Health & Related Research

A frequently reported problem with publicly funded randomised controlled trials is that the recruitment of participants is often slower or more difficult than expected, with many trials falling to reach their planned sample size within the originally envisaged trial timescale and trial funding envelope.

The United Kingdom’s National Institute for Health Research (NIHR) has funded studies that, at the design and application stage, have been overly optimistic about the number of eligible patients, consent rates, recruitment rates and retention/attrition rates. Consequently, these studies have failed to recruit on time and on target. The investigators have been forced to ask the NIHR programme for an extension in both time and extra money to successfully complete the study. A review of a cohort of 122 trials funded by the UK Medical Research Council and the NIHR Health Technology Assessment programme (HTA) found that less than a third (31%) of the trials achieved their original patient recruitment target; 55/122 (45.1%) achieved less than 80% of their original target and half (53%) were awarded an extension (McDonald et al 2006).

Funders such as the NIHR are now frequently asking for external pilot trials or internal pilot trials with stringent go/no go criteria to determine whether or not recruitment at the rate required for the main trial is feasible and sustainable within the trial timescale and trial funding envelope. So a question investigators and funders are now asking of statisticians is how long and large should the pilot phase of the RCT be in order to get a reasonable precise and stable estimate of the underlying recruitment rate for the proposed main RCT? In particular, how long should the pilot phase be? And how many centres should the pilot phase involve?

The proposed research plan would be to undertake a review of the literature on what factors influence recruitment to RCTs; as well as a review of the statistical literature on estimating recruitment rates from pilot studies and extrapolating this to the main trial.

The project would try and develop a statistical model to predict recruitment rates for the main RCT; based on pilot data; and compare this with the rates observed in several on-going RCTs at the Sheffield CTRU; with the view to developing guidance on how long should a pilot phase be; and how many centres should the pilot phase involve.

Entry Requirements

Candidates must have a first or upper second class honors degree in mathematics or statistics.

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Northern England