Inclusion, reporting and analysis of demographic variables in chronobiology and sleep research

Many aspects of sleep and circadian physiology appear to be sensitive to participant-level characteristics. While recent research robustly highlights the importance of considering participant-level demographic information, it is not clear to what extent this information is available within the large body of existing literature. This article investigates study sample characteristics within the published sleep and chronobiology research over the past 40 years. 6,777 articles were identified and a random sample of 20% was included. The reporting of sample size, age, sex, gender, ethnicity, level of education, socio-economic status, and profession of the study population was scored, and any reported aggregate summary statistics for these variables were recorded. We found that while >90% of studies reported age or sex, all other variables were reported in <25% of cases. Reporting quality was highly variable, indicating an opportunity to standardize reporting guidelines for participant-level characteristics to facilitate meta analyses. Summary In this article, we address the question of how representative, diverse and inclusive are published articles in sleep and chronobiology research. We analyzed a sample of >1300 articles published in sleep and chronobiology journals between 1979 and 2019 for its inclusion, reporting and analysis of study population characteristics, including age, sex, gender, race/ethnicity, level of education, socio-economic status, and profession. We found that while >90% of studies reported age or sex, all other variables were reported in <25% of cases, with the frequency of reporting changing over time. We identify opportunities for improving the reporting of demographic variables. Research Agenda Future research needs to: 1. Establish schemas for reporting demographic variables in a harmonized way across geographical and cultural contexts; 2. Identify gaps in the sleep and chronobiology literature with respect to understudied populations; 3. Understand the extent to which research practices allow for the inclusion of diverse populations in all stages of the research cycle, and how this can exacerbate health inequities. Practice Points 1. Published studies on circadian and sleep physiology should be carefully examined. 2. Reporting of demographic variables should be done deliberately and systematically. 3. Inclusion and diversity of different populations across the field needs to be ensured. ### Competing Interest Statement The authors have declared no competing interest.