# Dates and times

## Formats

There are three common formats across SAS, SPSS and Stata.

Date (number of days)

- SAS: MMDDYY, DDMMYY, YYMMDD, DATE
- Spss: n/a
- Stata: %td

Time (number of seconds):

- SAS: TIME, HHMM, TOD
- Spss: TIME, DTIME
- Stata: n/a

DateTime (number of seconds):

- SAS: DATETIME
- Spss: DATE, ADATE, SDATE, DATETIME (as milliseconds)
- Stata: %tc, %tC

## Offsets

Dates and date times use a difference offset to R:

- SAS: 1960-01-01 (3653 days)
- Spss: 1582-10-14. (141428 days)
- Stata: 1960-01-01. (3653 days)

## References

- SAS: https://v8doc.sas.com/sashtml/lrcon/zenid-63.htm, http://support.sas.com/documentation/cdl/en/etsug/60372/HTML/default/viewer.htm

- Spss: http://www-01.ibm.com/support/knowledgecenter/#!/SSLVMB_20.0.0/com.ibm.spss.statistics.help/idh_idd_dtwz_learn.htm http://www-01.ibm.com/support/knowledgecenter/#!/SSLVMB_20.0.0/com.ibm.spss.statistics.help/syn_date_and_time_date_time_formats.htm

- Stata: http://www.stata.com/manuals13/u24.pdf