When the INTERVAL= option is not specified in the ID statement, a time interval is inferred from the time ID values in the input data set. The technique used to infer a time interval involves searching for the interval that fits the greatest number of time ID values. First, time ID values are sampled from the input data set to generate a set of candidate intervals. Then the candidate interval that is consistent with greatest number of time ID values is chosen to represent the time series.

When the ALIGN=INFER option is specified, the convention that is used to specify time interval alignment is inferred from the time ID variable values by using a similar technique. When both the time interval and its alignment are to be inferred, each of the possible alignments, BEGIN, MIDDLE, and END, are considered in the search. Precedence in the search is given to intervals with the BEGIN alignment.