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. 2019 May 6;19(1):512.
doi: 10.1186/s12889-019-6820-3.

Calculating incidence rates and prevalence proportions: not as simple as it seems

Inge Spronk  1   2 , Joke C Korevaar  3 , René Poos  4 , Rodrigo Davids  3 , Henk Hilderink  4 , François G Schellevis  3   5 , Robert A Verheij  3 , Mark M J Nielen  3   4
Affiliations

Calculating incidence rates and prevalence proportions: not as simple as it seems

Inge Spronk et al. BMC Public Health. .

Abstract

Background: Incidence rates and prevalence proportions are commonly used to express the populations health status. Since there are several methods used to calculate these epidemiological measures, good comparison between studies and countries is difficult. This study investigates the impact of different operational definitions of numerators and denominators on incidence rates and prevalence proportions.

Methods: Data from routine electronic health records of general practices contributing to NIVEL Primary Care Database was used. Incidence rates were calculated using different denominators (person-years at-risk, person-years and midterm population). Three different prevalence proportions were determined: 1 year period prevalence proportions, point-prevalence proportions and contact prevalence proportions.

Results: One year period prevalence proportions were substantially higher than point-prevalence (58.3 - 206.6%) for long-lasting diseases, and one year period prevalence proportions were higher than contact prevalence proportions (26.2 - 79.7%). For incidence rates, the use of different denominators resulted in small differences between the different calculation methods (-1.3 - 14.8%). Using person-years at-risk or a midterm population resulted in higher rates compared to using person-years.

Conclusions: All different operational definitions affect incidence rates and prevalence proportions to some extent. Therefore, it is important that the terminology and methodology is well described by sources reporting these epidemiological measures. When comparing incidence rates and prevalence proportions from different sources, it is important to be aware of the operational definitions applied and their impact.

Keywords: Electronic health record; General practice; Incidence rate; Prevalence proportion.

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Conflict of interest statement

Ethics approval and consent to participate

Ethical approval according to the Medical Research (Human Subjects) Act (WMO), formal approval for this research project by a medical ethics committee was not required. The NIVEL Primary Care Database extracts data according to strict guidelines for the privacy protection of patients and GPs. In addition, we sought and obtained permission for this work from the board of the NIVEL network.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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