The 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 99.1 summarizes the designs, analysis criteria, hypotheses, and distributional assumptions supported in the TTEST procedure, along with the syntax used to specify them.
Table 99.1: Features Supported in the TTEST Procedure
|
Feature |
Syntax |
|---|---|
|
Design |
|
|
One-sample |
VAR statement |
|
Paired |
PAIRED statement |
|
Two-independent-sample |
|
|
AB/BA crossover |
|
|
Analysis Criterion |
|
|
Mean difference |
PROC TTEST TEST=DIFF |
|
Mean ratio |
PROC TTEST TEST=RATIO |
|
Hypothesis |
|
|
Two-sided |
|
|
Equivalence |
PROC TTEST TOST ( <lower ,> upper ) |
|
Lower one-sided |
|
|
Upper one-sided |
|
|
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.