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Exposure measurement error when assessing current glucocorticoid use using UK primary care electronic prescription data

Joseph, Rebecca M.; van Staa, Tjeerd P.; Lunt, Mark; Abrahamowicz, Michal; Dixon, William G.


Tjeerd P. van Staa

Mark Lunt

Michal Abrahamowicz

William G. Dixon


Purpose: To quantify misclassification in glucocorticoid (GC) exposure defined using UK primary care prescription data.
Methods: A cross‐sectional study including patients with rheumatoid arthritis prescribed oral GCs in the past 2 years. Glucocorticoid exposure based on electronic prescription records was compared with participant‐reported GC use captured using a paper diary. Prescription data (containing information about prescriptions issued but no dispensing information) was provided by the Clinical Practice Research Datalink. The following variables were defined: current use and dose of oral GCs and if (and when) participants had received a GC injection. For oral GCs, self‐reported use was taken to represent “true” exposure. A dataset representing a hypothetical population was generated to assess the impact of the misclassification found for current use.
Results: A total of 67 of 78 study participants (86%) were correctly classified as currently on/off oral GCs; 32/38 (84.2%) participants reporting current GC use and 35/40 (87.5%) participants not reporting current use were correctly classified. Estimated values of current dose were imprecise (correlation coefficient 0.46). Concordance between reported and prescribed GC injections was poor (kappa statistic 0.14). Misclassification bias was demonstrated in the hypothetical population: For “true” relative risks of 1.5, 4, and 9, the “observed” relative risks were 1.33, 2.48, and 3.58, respectively.
Conclusions: Misclassification of current use of oral GCs was low but sufficient to lead to significant bias. Researchers should take care to assess the likely impact of exposure misclassification on their analyses.


Joseph, R. M., van Staa, T. P., Lunt, M., Abrahamowicz, M., & Dixon, W. G. (2018). Exposure measurement error when assessing current glucocorticoid use using UK primary care electronic prescription data. Pharmacoepidemiology and Drug Safety, 28(2), 179-186.

Journal Article Type Article
Acceptance Date Aug 4, 2018
Online Publication Date Sep 28, 2018
Publication Date Sep 28, 2018
Deposit Date Feb 1, 2019
Publicly Available Date Feb 1, 2019
Journal Pharmacoepidemiology and Drug Safety
Print ISSN 1053-8569
Electronic ISSN 1099-1557
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 28
Issue 2
Pages 179-186
Keywords Pharmacology (medical); Epidemiology
Public URL
Publisher URL
Additional Information This paper was accepted on 4 August 2018 - before Rebecca Joseph moved to the University of Nottingham but was published as Gold Open Access.


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