The Index combines measures from multiple sources and perspectives to offer a broad view of the health protections in place for the nation as a whole and for each U.S. state. The Index identifies strengths as well as gaps in the protections needed to keep people safe and healthy in the face of large-scale public health threats, and it tracks how these protections vary across the United States and change over time.
I serve as a National Advisory Committee Member for the above. The measures do change over time because they are data based. Sometimes the collection of data ceases, thus there is no way to continue having the measure included. While there may be a bit of subjectivity, most of the measurement flows from data. The Advisory Committee reviews which measures should be deleted and added.