Following are miscellaneous questions about the data:
1. Are the years Y1, Y2, Y3, and Y4 calendar years, or some other 12-month periods?
2. Are the years Y1, Y2, Y3, and Y4 consecutive 12-month periods?
3. It is curious that the Heritage Provider Network has about 500,000 patients, but only about 70,000 patients per year are included in the data files. Thus, it is possible that the data may be a biased subset of the total population. How were the patients in the data selected?
4. What exactly is a "vendor"? Please give an example.
Thank you for your help.