BACKGROUND: Capturing changes in health and wellbeing within randomised controlled trials (RCTs) can be complex. The precision and accuracy of outcome scales to measure change is crucial, and therefore, consideration needs to be given to potential measurement errors when collecting these outcomes. Many RCTs use multiple researchers to collect data, which has the potential to introduce variation in measurements. This study aimed to identify if there was a measurable effect of using different researchers to collect repeated assessments of quality of life (QoL) at different time points.

METHODS: A previously conducted study assessing the impact of reminiscence therapy on participants with dementia and carer (PwD-carer) dyads, 'REMCARE' (Reminiscence groups for people with dementia and their family caregivers), provided the platform for this exploratory secondary analysis. Data was categorised into two broad groups: those where the same researcher attended all assessments and those where different researchers undertook the assessments. ANCOVA (analysis of covariance) models used in the original REMCARE analysis with the addition of the 'researcher-continuity' variable were run on two QoL measures, the QoL-AD (Quality of Life in Alzheimer's Disease) and QCPR (Quality of the Caregiving Relationship).

RESULTS: Three hundred thirty PwD-carer dyads were included in the analysis. For the PwD, a statistically significant effect was found on the researcher continuity variable for the QoL-AD and QCPR outcome measures at follow-up 1 but not at follow-up 2 signifying an impact of researcher attendance at the first follow-up but not follow-up 2. For the carer data, analyses revealed no statistically significant effects at follow-up 1; however, the QoL-AD measure at follow-up 2 was found to be statistically significant.

CONCLUSIONS: These exploratory results indicate the possible impact of researcher continuity on QoL outcomes in dementia studies. Further research is required to explore this further and establish causality. If demonstrated, this would have implications for the planning of future empirical studies in dementia, in order to reduce this potential source of bias.