The EXPAND procedure can be used to interpolate values for output series with different observation characteristics than the input series. To change observation characteristics, specify two values in the OBSERVED= option. The first value specifies the observation characteristics of the input series; the second value specifies the observation characteristics of the output series.

For example, the following statements convert the period total variable A in the data set ANNUAL to yearly midpoint estimates. This example does not change the series frequency, and the other variables in the data set are copied to the output data set unchanged.

   proc expand data=annual out=new from=year;
      id date;
      convert a / observed=(total,middle);
   run;