Pairing absolute and relative inequality measures for maternal and child health equity monitoring across 83 countries, 2010-2023: a cross-national ecological study

<title>Abstract</title> <p>Background Narrowing absolute wealth-related gaps can coexist with persistent proportional exclusion of the poorest groups. We assessed whether pairing the slope index of inequality (SII) with an endpoint-based poorest-to-richest coverage ratio (P:R ratio) could strengthen maternal and child health (MCH) equity monitoring using existing WHO data. Methods We conducted a cross-national ecological study using the WHO Health Inequality Data Repository. The analysis included 83 countries, eight MCH service indicators, and surveys conducted from 2010 to 2023. We analysed 1,651 country-indicator-year observations with both poorest- and richest-quintile estimates and 1,204 observations with valid SII estimates. The P:R ratio was Q1/Q5 coverage for favourable indicators and Q5/Q1 prevalence for ZeroDose. We paired SII and P:R classifications to identify double-burden and divergence countries. Operational concordance with the Relative Index of Inequality (RII) and incremental data yield were also assessed. Results Across 1,204 observations, the median absolute SII was 17.3 percentage points (IQR 6.4–37.0). Among 1,651 observations with endpoint data, 35.7% were classified as showing severe relative exclusion (P:R ratio &lt; 0.60). Twenty-one countries (25.3%) met double-burden criteria, with concentration in low- and lower-middle-income countries. Twelve divergence countries combined improvement in absolute SII with persistent majority Severe P:R classifications. Across 1,202 matched observations, P:R and RII classifications showed near-perfect concordance (weighted kappa = 0.896, 95% CI 0.879–0.913; exact agreement 85.4%). The P:R ratio was calculable for 447 additional observations. Conclusions Pairing SII with the P:R ratio distinguishes absolute-gap progress from proportional inclusion of the poorest groups. The ratio should be used as a transparent screening complement to SII and RII, not as a replacement for gradient-based measures or absolute coverage. This paired framework can make distributional progress more visible in MCH and universal health coverage monitoring without additional data collection.</p>