6. DATA SOURCES › 6.6 Notes on RMF Samples › 6.6.4 Sample Count Differences and Merging Files

6.6.4 Sample Count Differences and Merging Files

It is absolutely necessary to use the fffRSMP data elements
whenever files are combined by means of the MERGE With BY
facility in SAS, and calculations are then made based on
sample counts.

DO NOT USE the data element SAMPLES.  Due to skipped samples,
the value of the common data element SAMPLES in different
files may vary in records covering the same period of time.
Since the value of any SAS variable whose name is found in
more than one input file is determined by its value in the
last input file found in the MERGE statement, the ability to
recompute sampled statistics for data elements in other than
this last file is lost.

With the use of the fffRSMP data elements, whose identity and
value are not lost during the MERGE, these computations are
possible.  Be sure to use the correct one:  the file prefix
of both the measurement and the sample count data elements
must match.