Patient Perception, Preference and Participation Patient preferences and performance bias in a weight loss trial with a usual care arm §,§§

1. IntroductionPerformance bias refers to the conduct of a trial inadvertentlyintroducing differences between randomized groups other thanthe intervention(s) being evaluated. Such departures fromintended study design may compromise study aims by under-mining capacity to make valid inferences about interventioneffects. In healthcare contexts, staff provision of differential carewhen there is a lack of blinding about randomization statusconstitutes a classic example of this phenomenon. Indeeddifferential care has been included within the definition offeredby the Cochrane Collaboration as ‘‘systematic differences betweengroups in the care that is provided, or in exposure to factors otherthan the interventions of interest’’ [1]. Whilst considered in thecontext of systematic reviews [e.g. [2]] and related researchmethods texts, it is not obvious that this construct has itself beensubjected to empirical research scrutiny.Randomization is a somewhat unusual process as chance doesnot overtly govern many decisions in people’s lives, and this mayprovoke apprehension in advance or result in disappointment forsome trial participants [3]. Randomization is important in healthsciences and is widely used for good reasons, though paradoxicallyitsdirecteffectsarerarelymeasured[4].Placebocontrolconditionsare used in trials to manage the possible effects of disappointment,as well as to take account of the placebo effect itself [5]. Due toconcerns such as these, patient preference designs have beendevelopedtoavoidrandomizingparticipantswithstrongallocationpreferences to study conditions that would be disappointing [6].Some systematic reviews have identified capacity of preferences toimpact on trial outcomes [7] whereas others have not [8].Zelen designs have also been developed for situations whereseeking consent to be randomized may be problematic [9].Systematic reviews provide evidence of the use of Zelen andpatient