Patient groups and techniques change over time, assuming the data was even recorded in the first place. (eg. a lot of data from the past would not be useful today as a direct comparison or control group, simply because diets have changed so much.)
Patient groups and techniques change over time, assuming the data was even recorded in the first place. (eg. a lot of data from the past would not be useful today as a direct comparison or control group, simply because diets have changed so much.)