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*).