CDC weeks are numbered from one to 52 or 53. They start on Sunday. The first week of the year begins on the first calendar week that has at least four days in the new year. So, the Sunday in week 1 may land on Dec 29th, 30th, or 31st of the previous year. Every CDC week has 7 days and their can be 53 weeks. PROC EXPAND TO=WEEK calculates to weeks ending on Sunday. So, I should be able to use this as long as I format it with WEEKUw. The problem is that WEEKUw. starts week 1 on the first Sunday of the new year and includes week 0 for days of the new year before the first Sunday. So, there are weeks without 7 days which are made up for with week 53 in the previous year.
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