Time trends in demographic characteristics of participants and outcome measures in Parkinson's disease research: A 19-year single-center experience

Highlights•Parkinson’s disease studies historically focus on selective subgroups and motor symptoms.•We examined 33 Parkinson’s disease studies at a single center between 2003 and 2021.•We observed no temporal changes in adequate representation by sex, age or ethnicity.•It was equivocal whether assessment of non-motor symptoms increased over time.•Improved representation and non-motor assessments are warranted in future studies.AbstractBackgroundFemales, people with young-onset PD and older individuals, and non-white populations are historically underrepresented in clinical Parkinson’s disease (PD) research. Furthermore, research traditionally focused predominantly on motor symptoms of PD. Including a representative and diverse group of people with PD and also studying non-motor symptoms is warranted to better understand heterogeneity in PD and to generalize research findings.ObjectiveThis project aimed to determine whether, within a consecutive series of PD studies performed within a single center in the Netherlands: (1) the proportion of included females, mean age and proportion of native Dutch people changed over time; and 2) reports of the ethnicity of participants and the proportion of studies with non-motor outcomes changed over time.MethodsCharacteristics of participants and non-motor outcomes were analyzed using a unique dataset of summary statistics of studies with a large number of participants conducted at a single center during a 19-year period (2003–2021).ResultsResults indicate no relationship between calendar time and proportion of females (mean 39 %), mean age (66 years), proportion of studies that reported ethnicity, and proportion of native Dutch people in studies (range 97–100 %). The proportion of participants in whom non-motor symptoms were assessed increased, but this difference was consistent with chance.ConclusionStudy participants in this center reflect the PD population in the Netherlands in terms of sex, but older individuals and non-native Dutch individuals are under-represented. We have still a lot to do in ensuring adequate representation and diversity in PD patients within our research.