The Virginia Health Opportunity Index (HOI) consists of 13 indicators that act as the building blocks of the HOI. These indicators were chosen by our expert work group following an extensive review of the literature on the Social Determinants of Health (SDOH). Although there are innumerable variables and indicators that could be included, indicators were chosen based on the following criteria:
- Influence on health as expressed in the literature
- Input from Local Health Districts and other stakeholders
- Availability of data of consistent quality at the Census Tract level for all Census Tracts in Virginia
It is important to note that each indicator, the profiles, and the HOI itself, are conceived as indications of the opportunity to live a long and healthy life in each area. For instance, our indicator for Access to Care examines two variables: the percent of residents without health insurance and the number of full-time equivalent primary care physicians within 30 miles of the area. These two variables provide a good indication of access to care in each Census Tract. However, a more robust look would require examination of multiple variables, local dynamics and an understanding of the community. The HOI provides a roadmap for the Health Opportunity Landscape in an area but it does not tell the entire story.
With that caveat in mind, the HOI is remarkably predictive of health outcomes. Using spatially-weighted regression techniques, the HOI explains close to 60% of variation in Disability Free Life Expectancy (Healthy Life) in Virginia’s Census Tracts. This figure is similar to the influence many expect the SDOH has on health outcomes. The HOI was calibrated (checked for predictive value) using life expectancy, low birth weight, and disability free life expectancy in Virginia, and has proven predictive of specific diseases and health metrics in local areas.
To combine the multiple indicators, Z-scores were calculated for each indicator for each Census Tract in Virginia. Z-scores are a common standardization technique when using disparate data sources. These scores are weighted and combined using Principal Component Analysis into a single HOI score. The four profiles correspond to the four factors identified using Principal Component Analysis, and scores are a weighted combination of the relevant Z-scores. The HOI and the Profiles are further aggregated into simple quintiles corresponding to “very low”, “low”, “average”, “high” and “very high” opportunity levels by Census Tract. County-level HOI and profile scores are population-weighted averages of each indicator, combined using Principal Component weights as described above. Note that while the HOI and Profiles draw from the same set of indicators, differences in weighting means that the HOI and each Profile are stand-alone measures.
The variables and process used to develop each indicator are described in the following document, along with additional details on our methodology and calibration.