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Comparative Study
. 2013;8(3):e58593.
doi: 10.1371/journal.pone.0058593. Epub 2013 Mar 8.

Comparison and relative utility of inequality measurements: as applied to Scotland's child dental health

Yvonne I Blair  1 , Alex D McMahon, Lorna M D Macpherson
Affiliations
Comparative Study

Comparison and relative utility of inequality measurements: as applied to Scotland's child dental health

Yvonne I Blair et al. PLoS One. 2013.

Abstract

This study compared and assessed the utility of tests of inequality on a series of very large population caries datasets. National cross-sectional caries datasets for Scotland's 5-year-olds in 1993/94 (n = 5,078); 1995/96 (n = 6,240); 1997/98 (n = 6,584); 1999/00 (n = 6,781); 2002/03 (n = 9,747); 2003/04 (n = 10,956); 2005/06 (n = 10,945) and 2007/08 (n = 12,067) were obtained. Outcomes were based on the d3mft metric (i.e. the number of decayed, missing and filled teeth). An area-based deprivation category (DepCat) measured the subjects' socioeconomic status (SES). Simple absolute and relative inequality, Odds Ratios and the Significant Caries Index (SIC) as advocated by the World Health Organization were calculated. The measures of complex inequality applied to data were: the Slope Index of Inequality (absolute) and a variety of relative inequality tests i.e. Gini coefficient; Relative Index of Inequality; concentration curve; Koolman & Doorslaer's transformed Concentration Index; Receiver Operator Curve and Population Attributable Risk (PAR). Additional tests used were plots of SIC deciles (SIC(10)) and a Scottish Caries Inequality Metric (SCIM(10)). Over the period, mean d3mft improved from 3.1(95%CI 3.0-3.2) to 1.9(95%CI 1.8-1.9) and d3mft = 0% from 41.1(95%CI 39.8-42.3) to 58.3(95%CI 57.8-59.7). Absolute simple and complex inequality decreased. Relative simple and complex inequality remained comparatively stable. Our results support the use of the SII and RII to measure complex absolute and relative SES inequalities alongside additional tests of complex relative inequality such as PAR and Koolman and Doorslaer's transformed CI. The latter two have clear interpretations which may influence policy makers. Specialised dental metrics (i.e. SIC, SIC(10) and SCIM(10)) permit the exploration of other important inequalities not determined by SES, and could be applied to many other types of disease where ranking of morbidity is possible e.g. obesity. More generally, the approaches described may be applied to study patterns of health inequality affecting worldwide populations.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Prevalence of decayed, missing and filled teeth (%d3mft = 0) by SES for Scotland’s five-year-olds, 1993/94–2007/08.
Prevalence of decayed, missing and filled teeth (%d3mft = 0) by SES for Scotland’s five-year-olds, 1993/94–2007/08. (Change in overall distribution of d3mft, 2007/08 vs 1993/94, p<0.0001).
Figure 2
Figure 2. Slope Index of Inequality, Relative Index of Inequality and Population Attributable Risk for caries experience.
Slope Index of Inequality (SII) and Relative Index of Inequality (RII) for d3mft score and Population Attributable Risk (PAR) for caries experience (%d3mft>0) in Scotland’s 5-year-olds, 1993/94–2007/08.
Figure 3
Figure 3. Concentration curves and Receiver Operator Curve plots for decay experience by SES.
Concentration curves (CC) for d3mft scores (A) and Receiver Operator Curve (ROC) Plots for five-year-olds’ d3mft>0 (B) by SES (DepCat 2001) over the period 1993/94–2007/08.
Figure 4
Figure 4. Significant Caries Index deciles (SIC10) for Scotland’s 5-year-olds, 1993/94–2007/08.
See this image and copyright information in PMC

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