Weekly data: calendar week vs. Stata weeks

In my dataset, I have information on a number of workers for each week. The raw data I receive (no Stata format) contains information on the year and the week (1, 2, …, 52). Here, a week is defined as the first week of a year which has at least 4 days in January. E.g., the week 1/2009 starts already on December 29, 2008. A result of that is that for some years, a year has 53 calendar weeks. Continue reading

Managing time variables in Stata and SPSS

I just came across the problem that a date in Stata is not the same as a date in SPSS. They are, however, based on the same principle: time variables, e.g. a variable containing days, contain the number of elapsed time units (days, weeks, months, seconds, or other date units) since a base date which is defined by the software.

In Stata, the base date is the first time unit in 1960 (e.g. January 1, 1960). For other time units, Continue reading