
ALPHA=p

specifies that confidence intervals (except testbased mean confidence intervals when the TOST
option is used) are to be 100(1 – p)% confidence intervals, where 0 < p < 1. When the TOST
option is used, the testbased mean confidence intervals are 100(1 – 2p)% confidence intervals. By default, PROC TTEST uses ALPHA=
0.05. If p is 0 or less, or 1 or more, an error message is printed.

BYVAR

groups the results by the PAIRED
or VAR
variables. The BYVAR
option is enabled by default. Note that this represents a change from previous releases for how the results are grouped with
respect to variables and tables. Prior to SAS 9.2, multiple variables were included in each table, similar to the new NOBYVAR
option.

CI=EQUAL  UMPU  NONE
CL=EQUAL  UMPU  NONE

specifies whether a confidence interval is displayed for and, if so, what kind. The CI=
EQUAL option specifies an equaltailed confidence interval, and it is the default. The CI=
UMPU option specifies an interval based on the uniformly most powerful unbiased test of . The CI=
NONE option requests that no confidence interval be displayed for . The values EQUAL and UMPU together request that both types of confidence intervals be displayed. If the value NONE is specified
with one or both of the values EQUAL and UMPU, NONE takes precedence. For more information, see the section TwoIndependentSample Design.

COCHRAN

requests the Cochran and Cox (1950) approximation of the probability level for the unequal variances situation. For more information, see the section TwoIndependentSample Design.

DATA=SASdataset

names the SAS data set for the procedure to use. By default, PROC TTEST uses the most recently created SAS data set. The input
data set can contain summary statistics of the observations instead of the observations themselves. The number, mean, and
standard deviation of the observations are required for each BY
group (one sample and paired differences) or for each class within each BY
group (two samples). For more information about the DATA=
option, see the section Input Data Set of Statistics.

DIST=LOGNORMAL  NORMAL

specifies the underlying distribution assumed for the data. The default is NORMAL, unless TEST=
RATIO is specified, in which case the default is LOGNORMAL.

H0=m

requests tests against a null value of m, unless the TOST
option is used, in which case m is merely used to derive the lower and upper equivalence bounds. For the crossover design, the value m applies for both treatment and period tests. By default, PROC TTEST uses H0=
0 when TEST=
DIFF (or DIST=
NORMAL for a onesample design) and H0=
1 when TEST=
RATIO (or DIST=
LOGNORMAL for a onesample design).

NOBYVAR

includes all PAIRED
or VAR
variables together in each output table. If the NOBYVAR
option is not specified, then the BYVAR
option is enabled, grouping the results by the PAIRED
and VAR
variables.

ORDER=DATA  FORMATTED  FREQ  INTERNAL  MIXED

specifies the order in which to sort the levels of the classification variables (which are specified in the CLASS
statement) and treatment variables (which are specified in the CROSSOVER=
option in the VAR
statement). The default is ORDER=
MIXED, which corresponds to the ordering in releases previous to SAS 9.2.
This option applies to the levels for all classification or treatment variables, except when you use the ORDER=FORMATTED option
with numeric classification or treatment variables that have no explicit format. With this option, the levels of such variables
are ordered by their internal value.
The ORDER= option can take the following values:
Table 119.3: continued
Value of ORDER=

Levels Sorted By

DATA

Order of appearance in the input data set.

FORMATTED

External formatted value, except for numeric variables with no explicit format, which are sorted by their unformatted (internal)
value.

FREQ

Descending frequency count; levels with the most observations come first in the order. In the event of a tie, ORDER=
MIXED is used.

INTERNAL

Unformatted value.

MIXED

Same as ORDER=
FORMATTED if the unformatted variable is charactervalued; same as ORDER=
INTERNAL otherwise (the unformatted variable is numericvalued).

For FORMATTED and INTERNAL, the sort order is machinedependent.
For more information about sort order, see the chapter on the SORT procedure in the
Base SAS Procedures Guide and the discussion of BYgroup processing in
SAS Language Reference: Concepts.

PLOTS <(globalplotoptions)> <= plotrequest<(options)>>
PLOTS <(globalplotoptions)> <= (plotrequest<(options)> <... plotrequest<(options)>>)>

controls the plots produced through ODS Graphics. When you specify only one plotrequest, you can omit the parentheses around the plotrequest. Here are some examples:
plots=none
plots=(histogram boxplot interval qq profiles agreement)
plots(unpack)=summary
plots(showh0)=interval(type=pergroup)
plots=(summary(unpack) interval(type=period))
ODS Graphics must be enabled before plots can be requested. For example:
ods graphics on;
proc ttest plots=all;
var oxygen;
run;
ods graphics off;
For more information about enabling and disabling ODS Graphics, see the section Enabling and Disabling ODS Graphics in Chapter 21: Statistical Graphics Using ODS.
If ODS Graphics is enabled but you do not specify the PLOTS
option, then PROC TTEST produces a default set of plots. (
Note: The graphical results are unavailable if your input data set contains summary statistics rather than observation values.)
For a onesample design, the default plots are the following:
For a twoindependentsample design, the default plots are the following:
For a paired design, the default plots are the following:

summary plot (histogram, densities, box plot, and confidence interval) of the difference or ratio

QQ plot of the difference or ratio

profiles plot

agreement plot
For a crossover design, the default plots are the following:

comparative histograms with overlaid densities by treatment and period

comparative box plots by treatment and period

QQ plots by treatment and period

profiles over treatment plot

agreement of treatments plot
For more detailed descriptions of plots, see the section Interpreting Graphs.
The globalplotoptions include the following:

ONLY

suppresses the default plots. Only plots specifically requested are displayed.

SHOWH0
SHOWNULL

shows the null value (as specified by the H0=
option in the PROC TTEST
statement) in all relevant plots. For onesample and paired designs, the null value can appear in SUMMARY
, BOX
, and INTERVAL
. For twoindependentsample and crossover designs, the null value can appear only in INTERVAL
.

UNPACKPANEL
UNPACK

suppresses paneling. By default, multiple plots can appear in some output panels. Specify UNPACKPANEL
to get each plot in a separate panel. You can specify PLOTS
(UNPACKPANEL
) to unpack the default plots. You can also specify UNPACK
as a suboption with SUMMARY
.
The plotrequests include the following:

ALL

produces all appropriate plots. You can specify other options with ALL
; for example, to request all plots and specify that intervals should be for the period difference in a crossover design,
specify PLOTS
=(ALL
INTERVAL
(TYPE=
PERIOD)).

AGREEMENT
AGREEMENTPLOT

requests an agreement plot. This plot is produced by default for paired and crossover designs, the only designs for which
the AGREEMENT
option is valid.
For paired designs, the second response in each pair is plotted against the first response. See the section Agreement Plots for Paired Designs for further details.
For crossover designs, the AGREEMENT
plot request has the following options:

BOX
BOXPLOT

requests a box plot or comparative box plots. This plot is produced by default for crossover designs. For other designs, a
box plot appears as part of the SUMMARY
plot by default.
For onesample and paired designs, a confidence interval for the mean is shown as a band in the background, along with the
equivalence bounds if the TOST
option is used in the PROC TTEST
statement.
For a twoindependentsample design, comparative box plots (one for each class) are shown. For a crossover design, comparative
box plots for all four combinations of the two treatments and two periods are shown.
See the section Box Plots for further details.

HISTOGRAM
HIST
HISTDENS

requests a histogram or comparative histograms with overlaid normal and kernel densities. This plot is produced by default
for crossover designs. For other designs, it appears as part of the SUMMARY
plot by default.
For onesample and paired designs, the histogram and densities are based on the test criterion (which is the mean difference
or ratio for a paired design). For a twoindependentsample design, comparative histograms (one for each class) are shown.
For a crossover design, histograms for all four combinations of the two treatments and two periods are shown.
See the section Histograms for further details.

INTERVAL
INTERVALPLOT

requests plots of confidence interval for means.
For a twoindependentsample design, the INTERVAL
plot request has the following options:

TYPE=

PERGROUP shows two separate twosided confidence intervals, one for each class. This option cannot be used along with the
SHOWH0
global plot option.

TYPE=

TEST shows pooled and Satterthwaite confidence intervals. This is the default TYPE= option for twoindependentsample designs.
For a crossover design, The INTERVAL
plot request has the following options:

TYPE=

PERGROUP shows four separate twosided intervals, one for each treatmentbyperiod combination. This option cannot be used
along with the SHOWH0
global plot option.

TYPE=

PERIOD shows pooled and Satterthwaite confidence intervals for the period difference or ratio. This option is invalid if the
IGNOREPERIOD
option is used in the VAR
statement.

TYPE=

TREATMENT shows pooled and Satterthwaite confidence intervals for the treatment difference or ratio. This is the default TYPE=
option for crossover designs.
See the section Confidence Intervals for further details.

NONE

suppresses all plots.

PROFILES
PROFILESPLOT

requests a profiles plot. This plot is produced by default for paired and crossover designs, the only designs for which the
PROFILES
option is valid.
For paired designs, a line is drawn for each observation from left to right connecting the first response to the second response.
See the section Profiles for Paired Designs for further details.
For crossover designs, the PROFILES
plot request has the following options:

TYPE=

PERIOD shows response profiles over period, connecting the first period on the left to the second period on the right for
each subject. See the section Profiles over Period for Crossover Designs for further details.

TYPE=

TREATMENT shows response profiles over treatment values, connecting the first treatment on the left to the second treatment
on the right for each observation. This is the default TYPE= option for crossover designs. See the section Profiles over Treatment for Crossover Designs for further details.

QQ
QQPLOT

requests a normal quantilequantile (QQ) plot. This plot is produced by default for all designs.
For twosample designs, separate plots are shown for each class in a single panel. For crossover design, separate plots are
shown for each treatmentbyperiod combination in a single panel.
See the section QQ Plots for further details.

SUMMARY
SUMMARYPLOT

requests HISTOGRAM
and BOX
plots together in a single panel, sharing common X axes. This plot is produced by default for onesample, paired, and twoindependentsample
designs, the only designs for which the SUMMARY
option is valid. See the documentation for the BOX
and HISTOGRAM
plot requests for details. The SUMMARY
plot request has the following option:

UNPACK

plots histograms with overlaid densities in one panel and box plots (along with confidence interval bands, if onesample or
paired design) in another. Note that specifying PLOTS
(ONLY
)=SUMMARY
(UNPACK
) is exactly the same as specifying PLOTS
(ONLY
)=(BOX
HISTOGRAM
).

SIDES=2  L  U
SIDED=2  L  U
SIDE=2  L  U

specifies the number of sides (or tails) and direction of the statistical tests and testbased confidence intervals. The values
are interpreted as follows:
 2

(the default) specifies twosided tests and confidence intervals for means.
 L

specifies lower onesided tests, in which the alternative hypothesis indicates a mean less than the null value, and lower
onesided confidence intervals between minus infinity and the upper confidence limit.
 U

specifies upper onesided tests, in which the alternative hypothesis indicates a mean greater than the null value, and upper
onesided confidence intervals between the lower confidence limit and infinity.

TEST=DIFF  RATIO

specifies the test criterion. Use TEST=
DIFF to test the difference of means and TEST=
RATIO to test the ratio of means. The default is DIFF, unless DIST=
LOGNORMAL is specified, in which case the default is RATIO. This option is ignored for onesample designs.

TOST ( <lower ,> upper )

requests Schuirmann’s TOST equivalence test. The upper equivalence bound must be specified. If TEST=
DIFF, then the default value for the lower equivalence bound is upper, where m is the value of the H0=
option. If TEST=
RATIO, then the default value for lower is m / upper.