The TTEST Procedure

Overview: TTEST Procedure

The TTEST procedure performs t tests and computes confidence limits for one sample, paired observations, two independent samples, and the AB/BA crossover design. Two-sided, TOST (two one-sided test) equivalence, and upper and lower one-sided hypotheses are supported for means, mean differences, and mean ratios for either normal or lognormal data.

Table 119.1 summarizes the designs, analysis criteria, hypotheses, and distributional assumptions supported in the TTEST procedure, along with the syntax used to specify them.

Table 119.1: Features Supported in the TTEST Procedure

Feature

Syntax

Design

One-sample

VAR statement

Paired

PAIRED statement

Two-independent-sample

CLASS statement, VAR statement

AB/BA crossover

VAR / CROSSOVER=

Analysis Criterion

Mean difference

PROC TTEST TEST= DIFF

Mean ratio

PROC TTEST TEST= RATIO

Hypothesis

Two-sided

PROC TTEST SIDES= 2

Equivalence

PROC TTEST TOST ( <lower ,> upper )

Lower one-sided

PROC TTEST SIDES= L

Upper one-sided

PROC TTEST SIDES= U

Distribution

Normal

PROC TTEST DIST= NORMAL

Lognormal

PROC TTEST DIST= LOGNORMAL


FREQ and WEIGHT statements are available. Data can be input in the form of observations or, in certain cases, summary statistics. Output includes summary statistics; confidence limits for means, standard deviations, and coefficients of variation; hypothesis tests; and a variety of graphical displays, including histograms, densities, box plots, confidence intervals, Q-Q plots, profiles, and agreement plots.

PROC TTEST uses ODS Graphics to create graphs as part of its output. For general information about ODS Graphics, see Chapter 21: Statistical Graphics Using ODS. For specific information about the statistical graphics available with the TTEST procedure, see the PLOTS option in the PROC TTEST statement and the section ODS Graphics.