Assessing local chlamydia screening performance by combining survey and administrative data to account for differences in local population characteristics

Nathan Green,Catherine H Mercer,Clare Tanton,Ellie Sherrard-Smith,Peter J White,Pam Sonnenberg

doi:10.1038/s41598-019-43521-y

Abstract

Reducing health inequalities requires improved understanding of the causes of variation. Local-level variation reflects differences in local population characteristics and health system performance. Identifying low- and high-performing localities allows investigation into these differences. We used Multilevel Regression with Post-stratification (MRP) to synthesise data from multiple sources, using chlamydia testing as our example. We used national probability survey data to identify individual-level characteristics associated with chlamydia testing and combined this with local-level census data to calculate expected levels of testing in each local authority (LA) in England, allowing us to identify LAs where observed chlamydia testing rates were lower or higher than expected, given population characteristics. Taking account of multiple covariates, including age, sex, ethnicity, student and cohabiting status, 5.4% and 3.5% of LAs had testing rates higher than expected for 95% and 99% posterior credible intervals, respectively; 60.9% and 50.8% had rates lower than expected. Residual differences between observed and MRP expected values were smallest for LAs with large proportions of non-white ethnic populations. London boroughs that were markedly different from expected MRP values (≥90% posterior exceedance probability) had actively targeted risk groups. This type of synthesis allows more refined inferences to be made at small-area levels than previously feasible.

Highlights

Health inequalities are associated with social inequalities, which are strongly linked to geographic location[1]
The model indicated that the probability of chlamydia testing differed between ethnic groups, with Black, White and Mixed ethnic groups testing more than Asian, Chinese or people of undisclosed ethnicity; there were large uncertainties (Fig. 1)
In the case of chlamydia screening rates, we have shown a large variation amongst local authorities (LAs) in England, but there was large variation in the demographic composition of local authority (LA) populations and crude comparison of those that are above or below average, or even placing in to quintiles, does not indicate which LAs are performing better or worse than expected, given their populations

Summary

Introduction

Health inequalities are associated with social inequalities, which are strongly linked to geographic location[1]. In a similar way to using exceedance of ‘control limits’ on a funnel plot to identify outlier institutional performance[8], LAs with marked deviation of rates of recorded testing from expected rates obtained by MRP estimates could be investigated to learn reasons for their performance being lower or higher than expected, such as use of innovative approaches to providing access to testing[9] and in partner management[10]. This approach, to our knowledge, has never been used in an infectious disease context in England

Methods

Results

Conclusion