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Is an internal comparison better than using national data when estimating mortality in longitudinal studies?
T R Card1, M Solaymani-Dodaran, R Hubbard
1Division of Epidemiology and Public Health, University of Nottingham Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK. timcard@doctors.org.uk
Journal of Epidemiology and Community Health
|August 15, 2006
Summary
Cohort study methodology impacts mortality risk assessment. Using internal comparison groups provides more accurate mortality risk estimates than national population data for conditions like coeliac disease.
Area of Science:
- Epidemiology
- Biostatistics
Background:
- Methodological discrepancies in cohort studies can affect observed mortality risks.
- Investigating the impact of comparator group selection on outcome assessment is crucial.
Purpose of the Study:
- To evaluate the influence of different control groups on mortality risk estimates in cohort studies.
- To compare mortality risk in patients with inflammatory bowel disease, coeliac disease, and Barrett's oesophagus using matched controls versus national data.
Main Methods:
- Cohort studies utilized age, sex, practice, and calendar time-matched controls from the General Practice Research Database.
- Mortality data for England and Wales were sourced from the UK Office for National Statistics.
- Hazard ratios (HR) from matched controls were compared to standardized mortality ratios (SMR) derived from national data.
Main Results:
- Mortality risk was consistently underestimated when using national population data compared to internal matched controls.
- Specific findings included: coeliac disease HR 1.33 vs SMR 1.25; Barrett's oesophagus HR 1.32 vs SMR 1.32; inflammatory bowel disease HR 1.50 vs SMR 1.34.
Conclusions:
- A bias exists in cohort studies that underestimates mortality risk when using national death rates as a comparator.
- Internal comparison groups offer more appropriate and reliable estimates of mortality risk in cohort studies.