EPIWEEK: Stata module to create epidemiological week and equivalent epidemiological year

epiweek creates epidemiological week and equivalent epidemiological year from the calendar date. It extends the week function of Stata. Each epidemiological week begins on a Sunday and ends on Saturday. And the first epidemiological week of year ends on the first Saturday of January, provided that it falls at least four or more days into the month. epiweek2 converts epidemiological week and epidemiological year to the calendar date with the starting Sunday and the ending Saturday.