Letter to the Editor: Authors' Response.

Thank you for the opportunity to respond to the concerns of Dr Reneman and colleagues about our paper, Kersnovske et al. [13]. Dr Reneman and colleagues have raised two issues that we address below. Their first concern relates to the use of experts for the purpose of validation. We assume the authors are not concerned with the use of experts as a method of content validation, per se, as this is a well established and accept method of content validation. As noted by Portney and Watkins [14], “the determination of content validity is essentially a subjective process” (p. 83) and “claims for content validation are made by a panel of ’experts’ who review the instrumentation and determine if the questions satisfy the domain” (p. 83). It appears the issue is more with the operational definition of the “experts” in our panel. The term of expert is used in the content validation methodology literature and can be broadly interpreted. In an earlier stage of the content validation process, we subjected the Gibson approach to functional capacity evaluation (GAPP FCE) to more detailed review by a smaller selection of experts [7], indeed, “people with outstanding knowledge and experience”. For the item validity study we wanted a larger sample of different experts, including FCE practitioners with “known experience in, or relevant to, functional capacity evaluations”. Hence, the sample included practitioners known to be experienced in FCE as well as other experts from ergonomic and academic backgrounds and expertise.