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International Journal for Equity in Health

, 15:175

First Online: 19 October 2016Received: 08 June 2016Accepted: 26 September 2016DOI: 10.1186-s12939-016-0454-1

Cite this article as: Rodriguez-Caro, A., Vallejo-Torres, L. & Lopez-Valcarcel, B. Int J Equity Health 2016 15: 175. doi:10.1186-s12939-016-0454-1


BackgroundThere is a well-documented social gradient in obesity in most developed countries. Many previous studies have conventionally categorised individuals according to their body mass index BMI, focusing on those above a certain threshold and thus ignoring a large amount of the BMI distribution. Others have used linear BMI models, relying on mean effects that may mask substantial heterogeneity in the effects of socioeconomic variables across the population.

MethodIn this study, we measure the social gradient of the BMI distribution of the adult population in Spain over the past two decades 1993–2014, using unconditional quantile regressions. We use three socioeconomic variables education, income and social class and evaluate differences in the corresponding effects on different percentiles of the log-transformed BMI distribution. Quantile regression methods have the advantage of estimating the socioeconomic effect across the whole BMI distribution allowing for this potential heterogeneity.

ResultsThe results showed a large and increasing social gradient in obesity in Spain, especially among females. There is, however, a large degree of heterogeneity in the socioeconomic effect across the BMI distribution, with patterns that vary according to the socioeconomic indicator under study. While the income and educational gradient is greater at the end of the BMI distribution, the main impact of social class is around the median BMI values. A steeper social gradient is observed with respect to educational level rather than household income or social class.

ConclusionThe findings of this study emphasise the heterogeneous nature of the relationship between social factors and obesity across the BMI distribution as a whole. Quantile regression methods might provide a more suitable framework for exploring the complex socioeconomic gradient of obesity.

KeywordsObesity Social inequalities Unconditional quantile regression AbbreviationsBMIBody mass index

CQRConditional quantile regression

OLSOrdinary least squares

RIFRecentered influence function

UQRUnconditional quantile regression

Electronic supplementary materialThe online version of this article doi:10.1186-s12939-016-0454-1 contains supplementary material, which is available to authorized users.

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Autor: Alejandro Rodriguez-Caro - Laura Vallejo-Torres - Beatriz Lopez-Valcarcel

Fuente: https://link.springer.com/

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