A statistical test for the equality of differently adjusted incidence rate ratios.
An incidence rate ratio (IRR) is a meaningful effect measure in epidemiology if it is adjusted for all important confounders. For evaluation of the impact of adjustment, adjusted IRRs should be compared with crude IRRs. The aim of this methodological study was to present a statistical approach for testing the equality of adjusted and crude IRRs and to derive a confidence interval for the ratio of the two IRRs. The method can be extended to compare two differently adjusted IRRs and, thus, to evaluate the effect of additional adjustment. The method runs immediately on existing software. To illustrate the application of this approach, the authors studied adjusted IRRs for two risk factors of type 2 diabetes using data from the European Prospective Investigation into Cancer and Nutrition-Potsdam Study from 2005. The statistical method described may be helpful as an additional tool for analyzing epidemiologic cohort data and for interpreting results obtained from Cox regression models with adjustment for different covariates.
Hoffmann
Kurt
K
Department of Epidemiology, German Institute of Human Nutrition Potsdam-Rehbrücke, Nuthetal, Germany.
Pischon
Tobias
T
Schulz
Mandy
M
Schulze
Matthias B
MB
Ray
Jennifer
J
Boeing
Heiner
H
D000328:Adult; D015331:Cohort Studies; D016001:Confidence Intervals; D015986:Confounding Factors, Epidemiologic; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D004812:Epidemiologic Methods; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D016016:Proportional Hazards Models; D020379:Risk Adjustment; D018570:Risk Assessment / Q000379:methods / Q000706:statistics & numerical data*; D012307:Risk Factors; D011795:Surveys and Questionnaires