Early studies tended to use logistic regression methods for binary mortality status at the end of the follow-up period. These models report odds ratios (OR). Most recent studies use more sensitive Cox proportional hazards methods for analysis of time to death. These models report hazard ratios (HR). The method of analysis does not appear to affect the significance of the results.

This has become an extremely well-replicated finding in a very short time, considering that the studies are prospective and have quite long follow-up periods. Most or all of the studies would be considered "secondary analysis" of data (the data were collected initially for another purpose). Because self-ratings of health are so commonly used in surveys, there were many available data files with the necessary elements for the analysis, and hence a large number of studies have appeared.