A methodology for small area prevalence estimation based on survey data

Abstract

Background: Brazil conducts many health surveys to provide estimates by national level, macro-regions, states, metropolitan regions and capitals. However, estimates for smaller areas are lacking due to their high cost. The Health Vulnerability Index (in Portuguese, Índice de Vulnerabilidade em Saúde, IVS) is a measure that combines socioeconomic and environmental variables in the same indicator and allows for the analysis of the characteristics of population groups residing in census tracts, grouping them into four health risk areas (low, medium, high and very high risk) in addition to showing inequalities in the epidemiological profile of different social groups. This index was developed by the Municipal Health Secretariat of Belo Horizonte to guide health planning. Objective: The aim of the study is to produce a methodology for obtaining reliable estimates for tobacco smoking in small areas for which the IVS was not designed. Methods: The Vigitel dataset from 2006 to 2013 was used to obtain estimates of the prevalence of smokers based on the IVS employing small area estimation methods that use data from a larger domain to obtain estimates in smaller areas. For indirect estimates, the covariates included were sanitation, housing, education, income, and social and health factors. Post-stratification weights were used according to the IVS based on the population of the 2010 census. Results: From 2006 to 2009, 16.2% (95% CI: 13.6-14.8%) of the adult population in Belo Horizonte were smokers, and 14.8% (95% CI: 14.0-15.6%) were smokers between 2010 and 2013. The very high-risk population maintained a high prevalence over the same period of 21.1% (95% CI: 17.1-25.0%) between 2006 and 2009 and 20.8% (95% CI: 17.0-24.6%) between 2010 and 2013, while in the low-risk group, the prevalence in the same period fell from 14.9% (95% CI: 13.7-16.2%) to 11.8% (95% CI, 10.6-13.1%). Conclusions: The present study identified differences in the profile of smokers by the IVS in the city of Belo Horizonte. While the smoking prevalence declined in richer areas, it remained high in poor areas. This methodology can be used to produce reliable estimates for subgroups with greater vulnerability in small areas and thus subsidize the formulation, monitoring and evaluation of public health policies and programmes aimed at smoking.

Fruit and vegetable consumption, leisure-time physical activity and binge drinking in Belo Horizonte, Brazil, according to the Health Vulnerability Index

“…. More detailed information on the direct method of estimation for small areas employed can be obtained in another publication 10 . The difference in the prevalence of regular FV consumption, LTPA practice, and binge drinking between the IVS groups was statistically verified by the Student's t-test, with a significance level of 5%.…”

“…Brazil has national surveys that make it possible to measure numerous health events. However, due to costs, the sampling used generally estimates large areas, such as the Federated Units, reaching up to the capitals at most, failing to estimate small areas, nor identifying intra-urban inequalities 10 . Thus, it is necessary to advance the knowledge of the differences in the distribution of health events in different population groups, aiming to support policies to reduce inequalities in health 11 .…”

Estimates of hypertension and diabetes mellitus prevalence according to Health Vulnerability Index in Belo Horizonte, MG, Brazil

“…NCD and their risk factors have been monitored in the country by large national surveys, which are essential to aggregate evidence on individual and collective health 6,7 ; however, national surveys do not allow estimates by municipalities or for smaller areas within the sampled cities. Thus, it is necessary to advance the monitoring of these diseases in small geographic areas, in order to identify the existing inequalities, which are often masked by national or state average statistics 8,9 .…”

“…Estimates for small areas can help managers in public health in planning, defining intervention priorities and allocating resources, in addition to identifying possible decentralized solutions to the diagnosed problems, which may include social, cultural, legal, political or health-related approaches in small areas 8,9 . The use of composite indicators in the health RESUMO: Objetivo: Estimar as prevalências de hipertensão e diabetes para pequenas áreas em Belo Horizonte, MG, segundo o índice de vulnerabilidade da saúde (IVS).…”

Understanding inequities in health and health systems in Latin America and the Caribbean: a thematic series

“…Moreover, high-quality methodologies can help assess the impact of health policies with greater precision. The paper by Tomie Ivata Bernal et al [ 16 ] illustrates how the use of a small-area prevalence estimation identified that the reduction in tobacco prevalence in Brazil was more common in high-income areas than it was in the lower-income areas. The ability to replicate these approaches to use more granular information may foster better local policies.…”