Age-related selection bias in Parkinson's disease research: are we recruiting the right participants?

Angus D. MacLeod, Rachel Henery, Paul C. Nwajiugo, Nicholas W. Scott, Robert Caslake, Carl E. Counsell

Research output: Contribution to journalArticle

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Abstract

Objective:

To describe, and explore heterogeneity in, age at onset/diagnosis in Parkinson’s disease (PD) and compare mean age at onset/diagnosis in incidence studies with that in general PD research studies.

Methods:

We systematically reviewed studies of PD incidence. We meta-analysed mean age at onset/diagnosis and age-stratum-specific incidence rates. We compared age-specific incidence rates in screening studies in the elderly with whole-population studies. We collated mean ages at onset/diagnosis in clinical studies of PD in five journals July–December 2016.

Results:

In 17 studies reporting sufficient data to pool, mean age at onset/diagnosis was 69.6 years (95% CI 68.2–71.1), but heterogeneity was high (I2=96%). In ten of these studies reporting age at diagnosis specifically, the pooled mean age at diagnosis was slightly higher (71.6 [95% CI 70.6–72.6]) with lower, but still high, heterogeneity (I2=84%). In twelve whole-population studies reporting age-specific incidence rates, these peaked in age 70-79 (pooled incidence rate per 100,000=93.8 [95% CI 80.3–107.6]). Heterogeneity increased with each increase in age stratum (0% in youngest to 88% in oldest age stratum). Pooled age-specific incidence rates in five population-based screening studies of older age groups were several-fold higher than in whole-population studies. The mean of the reported mean ages at onset/diagnosis in recently published research studies was 60.8 (SD 5.6).

Conclusion:

The mean age of onset/diagnosis PD is about 70, although this may be an underestimate due to under-diagnosis in the elderly. Many published studies use age-unrepresentative subjects: the effect of this selection bias deserves further study.
Original languageEnglish
Pages (from-to)128-133
Number of pages6
JournalParkinsonism & Related Disorders
Volume55
Early online date31 May 2018
DOIs
Publication statusPublished - Oct 2018

Fingerprint

Selection Bias
Parkinson Disease
Age of Onset
Research
Incidence
Age Factors
Population
Cohort Studies
Research Design
Age Groups

Keywords

  • Parkinson's Disease
  • age
  • selection bias
  • incidence studies
  • systematic review

Cite this

Age-related selection bias in Parkinson's disease research : are we recruiting the right participants? / MacLeod, Angus D.; Henery, Rachel; Nwajiugo, Paul C.; Scott, Nicholas W.; Caslake, Robert; Counsell, Carl E.

In: Parkinsonism & Related Disorders, Vol. 55, 10.2018, p. 128-133.

Research output: Contribution to journalArticle

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abstract = "Objective: To describe, and explore heterogeneity in, age at onset/diagnosis in Parkinson’s disease (PD) and compare mean age at onset/diagnosis in incidence studies with that in general PD research studies.Methods:We systematically reviewed studies of PD incidence. We meta-analysed mean age at onset/diagnosis and age-stratum-specific incidence rates. We compared age-specific incidence rates in screening studies in the elderly with whole-population studies. We collated mean ages at onset/diagnosis in clinical studies of PD in five journals July–December 2016.Results:In 17 studies reporting sufficient data to pool, mean age at onset/diagnosis was 69.6 years (95{\%} CI 68.2–71.1), but heterogeneity was high (I2=96{\%}). In ten of these studies reporting age at diagnosis specifically, the pooled mean age at diagnosis was slightly higher (71.6 [95{\%} CI 70.6–72.6]) with lower, but still high, heterogeneity (I2=84{\%}). In twelve whole-population studies reporting age-specific incidence rates, these peaked in age 70-79 (pooled incidence rate per 100,000=93.8 [95{\%} CI 80.3–107.6]). Heterogeneity increased with each increase in age stratum (0{\%} in youngest to 88{\%} in oldest age stratum). Pooled age-specific incidence rates in five population-based screening studies of older age groups were several-fold higher than in whole-population studies. The mean of the reported mean ages at onset/diagnosis in recently published research studies was 60.8 (SD 5.6).Conclusion:The mean age of onset/diagnosis PD is about 70, although this may be an underestimate due to under-diagnosis in the elderly. Many published studies use age-unrepresentative subjects: the effect of this selection bias deserves further study.",
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author = "MacLeod, {Angus D.} and Rachel Henery and Nwajiugo, {Paul C.} and Scott, {Nicholas W.} and Robert Caslake and Counsell, {Carl E.}",
note = "Acknowledgements We acknowledge the earlier work of Dr Kate Taylor and Dr Dominique Twelves on the previous systematic review of incidence studies in Parkinson’s disease. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Authors report the following funding received during the conduct of this study: Dr Macleod: fellowship funding from the Chief Scientist Office of the Scottish Government and NHS Education for Scotland; grant funding Parkinson’s UK, the Academy of Medical Sciences, NHS Grampian Endowments, the Wellcome Trust, the University of Aberdeen. Dr Henery: financial support from the University of Aberdeen Dr Nwajiugo: none Dr Scott: none Dr Caslake: grant funding from Parkinson’s UK Dr Counsell: grant funding from the Chief Scientist Office of the Scottish Government, the PSP Association, and NHS Grampian Endowments.",
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AU - MacLeod, Angus D.

AU - Henery, Rachel

AU - Nwajiugo, Paul C.

AU - Scott, Nicholas W.

AU - Caslake, Robert

AU - Counsell, Carl E.

N1 - Acknowledgements We acknowledge the earlier work of Dr Kate Taylor and Dr Dominique Twelves on the previous systematic review of incidence studies in Parkinson’s disease. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Authors report the following funding received during the conduct of this study: Dr Macleod: fellowship funding from the Chief Scientist Office of the Scottish Government and NHS Education for Scotland; grant funding Parkinson’s UK, the Academy of Medical Sciences, NHS Grampian Endowments, the Wellcome Trust, the University of Aberdeen. Dr Henery: financial support from the University of Aberdeen Dr Nwajiugo: none Dr Scott: none Dr Caslake: grant funding from Parkinson’s UK Dr Counsell: grant funding from the Chief Scientist Office of the Scottish Government, the PSP Association, and NHS Grampian Endowments.

PY - 2018/10

Y1 - 2018/10

N2 - Objective: To describe, and explore heterogeneity in, age at onset/diagnosis in Parkinson’s disease (PD) and compare mean age at onset/diagnosis in incidence studies with that in general PD research studies.Methods:We systematically reviewed studies of PD incidence. We meta-analysed mean age at onset/diagnosis and age-stratum-specific incidence rates. We compared age-specific incidence rates in screening studies in the elderly with whole-population studies. We collated mean ages at onset/diagnosis in clinical studies of PD in five journals July–December 2016.Results:In 17 studies reporting sufficient data to pool, mean age at onset/diagnosis was 69.6 years (95% CI 68.2–71.1), but heterogeneity was high (I2=96%). In ten of these studies reporting age at diagnosis specifically, the pooled mean age at diagnosis was slightly higher (71.6 [95% CI 70.6–72.6]) with lower, but still high, heterogeneity (I2=84%). In twelve whole-population studies reporting age-specific incidence rates, these peaked in age 70-79 (pooled incidence rate per 100,000=93.8 [95% CI 80.3–107.6]). Heterogeneity increased with each increase in age stratum (0% in youngest to 88% in oldest age stratum). Pooled age-specific incidence rates in five population-based screening studies of older age groups were several-fold higher than in whole-population studies. The mean of the reported mean ages at onset/diagnosis in recently published research studies was 60.8 (SD 5.6).Conclusion:The mean age of onset/diagnosis PD is about 70, although this may be an underestimate due to under-diagnosis in the elderly. Many published studies use age-unrepresentative subjects: the effect of this selection bias deserves further study.

AB - Objective: To describe, and explore heterogeneity in, age at onset/diagnosis in Parkinson’s disease (PD) and compare mean age at onset/diagnosis in incidence studies with that in general PD research studies.Methods:We systematically reviewed studies of PD incidence. We meta-analysed mean age at onset/diagnosis and age-stratum-specific incidence rates. We compared age-specific incidence rates in screening studies in the elderly with whole-population studies. We collated mean ages at onset/diagnosis in clinical studies of PD in five journals July–December 2016.Results:In 17 studies reporting sufficient data to pool, mean age at onset/diagnosis was 69.6 years (95% CI 68.2–71.1), but heterogeneity was high (I2=96%). In ten of these studies reporting age at diagnosis specifically, the pooled mean age at diagnosis was slightly higher (71.6 [95% CI 70.6–72.6]) with lower, but still high, heterogeneity (I2=84%). In twelve whole-population studies reporting age-specific incidence rates, these peaked in age 70-79 (pooled incidence rate per 100,000=93.8 [95% CI 80.3–107.6]). Heterogeneity increased with each increase in age stratum (0% in youngest to 88% in oldest age stratum). Pooled age-specific incidence rates in five population-based screening studies of older age groups were several-fold higher than in whole-population studies. The mean of the reported mean ages at onset/diagnosis in recently published research studies was 60.8 (SD 5.6).Conclusion:The mean age of onset/diagnosis PD is about 70, although this may be an underestimate due to under-diagnosis in the elderly. Many published studies use age-unrepresentative subjects: the effect of this selection bias deserves further study.

KW - Parkinson's Disease

KW - age

KW - selection bias

KW - incidence studies

KW - systematic review

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DO - 10.1016/j.parkreldis.2018.05.027

M3 - Article

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SP - 128

EP - 133

JO - Parkinsonism & Related Disorders

JF - Parkinsonism & Related Disorders

SN - 1353-8020

ER -