PROC TTEST accepts data containing either observation values or summary statistics. Observation values are supported for all analyses, whereas summary statistics are supported only for a subset of analyses. If the analysis involves the paired design, the AB/BA crossover design, or the lognormal distributional assumption (DIST=LOGNORMAL), then observation values must be used. The graphical results are unavailable if your input data set contains summary statistics rather than raw observed values.

PROC TTEST assumes that the DATA= data set contains statistics if it contains a character variable with name `_TYPE_`

or `_STAT_`

. The TTEST procedure expects this character variable to contain the names of statistics. If both `_TYPE_`

and `_STAT_`

variables exist and are of type character, PROC TTEST expects `_TYPE_`

to contain the names of statistics including ‘N’, ‘MEAN’, and ‘STD’ for each BY group (or for each class within each BY group for two-sample t tests). If no ‘N’, ‘MEAN’, or ‘STD’ statistics exist, an error message is printed.

FREQ, WEIGHT, and PAIRED statements cannot be used with input data sets of statistics. BY, CLASS, and VAR statements are the same regardless of data set type. For paired comparisons, see the `_DIF_`

values for the `_TYPE_`

=T observations in output produced by the OUTSTATS= option in the PROC COMPARE statement (see the
*Base SAS Procedures Guide*).