Background
It is good practice to feedback clinically relevant findings to study participants where the benefit outweighs any potential harm [However, providing participants with their individual health results is challenging and costly to do well [What we do not know, however, is how feeding back clinically relevant findings may affect participation in longitudinal studies [This paper investigates whether offering feedback from blood samples as part of an ongoing longitudinal study influenced participants’ willingness to give blood samples and to take part in the study overall, both at the wave the samples are taken and in the subsequent follow up wave. Secondly, it investigates whether feedback had a differential impact on consent to a blood sample in the different modes (web v interviewer v nurse interview) and based on the length of time a participant had been in the study. Finally, the paper explores whether different social and demographic groups respond differently to the offer of feedback.