Output Data Sets

The FREQ Procedure

Output Data Sets

PROC FREQ produces two types of output data sets that you can use with other statistical and reporting procedures. These data sets are produced as follows:

specifying a TABLES statement with an OUT= option creates an output data set that contains frequency or crosstabulation table counts and percentages.
specifying an OUTPUT statement creates an output data set that contains statistics.

PROC FREQ does not display the output data sets. Use PROC PRINT, PROC REPORT, or any other SAS reporting tool to display an output data set.

Contents of the TABLES Statement Output Data Set

The OUT= option in the TABLES statement creates an output data set that contains one observation for each combination of the variable values (or table cell) in the last table request. By default, each observation contains the frequency and percentage for the table cell. When the input data set contains missing values, the output data set also contains an observation with the frequency of missing values. The output data set includes the following variables:

BY variables
table request variables, such as A, B, C, and D in the table request A*B*C*D
COUNT, a variable containing the cell frequency
PERCENT, a variable containing the cell percentage

If you specify the OUTEXPECT and OUTPCT options in the TABLES statement, the output data set also contains expected frequencies and row, column, and table percentages, respectively. The additional variables are

EXPECTED, a variable containing the expected frequency
PCT_TABL, a variable containing the percentage of two-way table frequency, for n-way tables where n > 2
PCT_ROW, a variable containing the percentage of row frequency
PCT_COL, a variable containing the percentage of column frequency

When you submit the following statements

    proc freq;
       tables A A*B / out=D;
    run;

the output data set D contains frequencies and percentages for the last table request, A*B. If A has two levels (1 and 2), B has three levels (1,2, and 3), and no table cell count is zero or missing, the output data set D includes six observations, one for each combination of A and B. The first observation corresponds to A=1 and B=1; the second observation corresponds to A=1 and B=2; and so on. The data set includes the variables COUNT and PERCENT. The value of COUNT is the number of observations with the given combination of A and B values. The value of PERCENT is the percent of the total number of observations having that A and B combination.

When PROC FREQ combines different variable values into the same formatted level, the output data set contains the smallest internal value for the formatted level. For example, suppose a variable X has the values 1.1., 1.4, 1.7, 2.1, and 2.3. When you submit the statement

    format X 1.;

in a PROC FREQ step, the formatted levels listed in the frequency table for X are 1 and 2. If you create an output data set with the frequency counts, the internal values of X are 1.1 and 1.7. To report the internal values of X when you display the output data set, use a format of 3.1 with X.

Contents of the OUTPUT Statement Output Data Set

The OUTPUT statement creates a SAS data set containing the statistics that PROC FREQ computes for the last table request. You specify which statistics to store in the output data set. There is an observation with the specified statistics for each stratum or two-way table. If PROC FREQ computes summary statistics for a stratified table, the output data set also contains a summary observation with those statistics.

The OUTPUT data set can include the following variables.

BY variables
variables that identify the stratum, such as A and B in the table request A*B*C*D
variables that contain the specified statistics

The output data set also includes variables with the p-values and degrees of freedom, asymptotic standard error (ASE), or confidence limits when PROC FREQ computes these values for a specified statistic.

The variable names for the specified statistics in the output data set are the names of the options enclosed in underscores. PROC FREQ forms variable names for the corresponding p-values, degrees of freedom, or confidence limits by combining the name of the option with the appropriate prefix from the following list:

DF_ degrees of freedom

E_ asymptotic standard error (ASE)

L_ lower confidence limit

U_ upper confidence limit

E0_ ASE under the null hypothesis

Z_ standardized value

P_ p-value

P2_ two-sided p-value

PL_ left-sided p-value

PR_ right-sided p-value

XP_ exact p-value

XP2_ exact two-sided p-value

XPL_ exact left-sided p-value

XPR_ exact right-sided p-value

XL_ exact lower confidence limit

XR_ exact upper confidence limit

For example, variable names created for the Pearson chi-square, its degrees of freedom, its p-values are _PCHI_, DF_PCHI, and P_PCHI, respectively.

If the length of the prefix plus the statistic option exceeds eight characters, PROC FREQ truncates the option so that the name of the new variable is eight characters long.

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DF_	degrees of freedom
E_	asymptotic standard error (ASE)
L_	lower confidence limit
U_	upper confidence limit
E0_	ASE under the null hypothesis
Z_	standardized value
P_	p-value
P2_	two-sided p-value
PL_	left-sided p-value
PR_	right-sided p-value
XP_	exact p-value
XP2_	exact two-sided p-value
XPL_	exact left-sided p-value
XPR_	exact right-sided p-value
XL_	exact lower confidence limit
XR_	exact upper confidence limit