Pearls, Pith, and Provocation Patient and public involvement in health care research

der et al., 2004) and is now a requirement in most publi-cally funded research in the United Kingdom (Department of Health, 2006). The recent history of active involve-ment in the research process of people who use health and social care services is well documented and has begun to be systematically evaluated (Staley, 2009). The involve-ment of mental health service users in research has been particularly well described (Sweeney, Beresford, Faulkner, Nettle, & Rose, 2009). It has been argued that, given the expertise that people experiencing mental health problems have in managing their lives (Faulkner & Layzell, 2000), building an evi-dence base for mental health services should be con-ducted as a marriage of expertise by experience and expertise by profession (Faulkner & Thomas, 2002). The difficulties of assessing the epistemological impact on the research process of involving service users have been acknowledged (Smith et al., 2008; Staley, 2009). Without this insight, the knowledge claims of research involvin