Dataset showing life expectancy at birth reflects the overall mortality level of the population. It summarizes the mortality pattern that prevails across all age groups - children and adolescents, adults and the elderly. Life expectancy is expressed as the average number of years that a newborn is expected to live if current mortality rates continue to apply.

Premature death rate measures mortality by counting deaths at earlier ages more than deaths at later ages. For example, when a person dies at 20, this death contributes 55 years of potential life lost. In contrast, when a person dies at age 70, this death contributes only five years of potential life lost to a county. For our purposes, premature deaths occur before age 75. Counties with older populations are more likely to have higher crude premature death rates than counties with younger populations. Therefore, when age-adjusted, we remove the effect of differently aged populations as a risk factor for premature death. This allows us to make a fair comparison of premature death rates across counties.