Relative index of inequality

Relative Index of Inequality

The Relative Index of Inequality (RII) is a measure used in epidemiology and public health to quantify the degree of inequality in health outcomes across different socioeconomic groups. It is a relative measure, meaning it compares the health status of individuals at different points in the socioeconomic hierarchy.

Concept and Calculation

The RII is calculated by ranking individuals or groups according to their socioeconomic status (SES) and then assessing the relationship between this ranking and a health outcome. The RII is typically derived from a regression model where the health outcome is regressed on the ranked SES variable. The RII value indicates the extent to which health outcomes differ across the socioeconomic spectrum.

The formula for calculating the RII involves:

1. Ranking individuals or groups from the lowest to the highest SES. 2. Assigning a relative rank to each group, often scaled between 0 and 1. 3. Using regression analysis to estimate the association between the relative rank and the health outcome.

Interpretation

An RII value greater than 1 indicates that health outcomes are worse among those with lower SES compared to those with higher SES. Conversely, an RII value less than 1 suggests that health outcomes are better among those with lower SES. An RII of 1 implies no inequality in health outcomes across the socioeconomic spectrum.

Applications

The RII is widely used in public health research to:

• Assess health inequalities within populations.
• Monitor changes in health inequalities over time.
• Evaluate the impact of policies aimed at reducing health disparities.

Limitations

While the RII is a useful tool for measuring health inequalities, it has some limitations:

• It requires accurate data on both health outcomes and socioeconomic status.
• It assumes a linear relationship between SES and health outcomes, which may not always be the case.
• It may not capture inequalities within subgroups of the population.

Related Concepts

The RII is related to other measures of inequality, such as the Concentration Index and the Slope Index of Inequality. These measures also assess the distribution of health outcomes across socioeconomic groups but differ in their methodological approaches and interpretations.