The SURVEYFREQ Procedure

PROC SURVEYFREQ Statement

PROC SURVEYFREQ <options> ;

The PROC SURVEYFREQ statement invokes the SURVEYFREQ procedure. It also identifies the data set to be analyzed, specifies the variance estimation method to use, and provides sample design information. The DATA= option names the input data set to be analyzed. The VARMETHOD= option specifies the variance estimation method, which is the Taylor series method by default. For Taylor series variance estimation, you can include a finite population correction factor in the analysis by providing either the sampling rate or population total in the RATE= or TOTAL= option, respectively. If your design is stratified with different sampling rates or totals for different strata, you can input these stratum rates or totals in a SAS data set that contains the stratification variables.

Table 111.1 summarizes the options available in the PROC SURVEYFREQ statement.

Table 111.1: PROC SURVEYFREQ Statement Options

Option	Description
DATA=	Names the input SAS data set
MISSING	Treats missing values as a valid level
NOMCAR	Treats missing values as not missing completely at random
NOSUMMARY	Suppresses the display of the "Data Summary" table
ORDER=	Specifies the order of variable levels
PAGE	Displays only one table per page
RATE=	Specifies the first-stage sampling rate
TOTAL=	Specifies the total number of primary sampling units
VARHEADER=	Specifies the variable identification to display
VARMETHOD=	Specifies the variance estimation method

You can specify the following options:

DATA=SAS-data-set

names the SAS-data-set to be analyzed by PROC SURVEYFREQ. If you omit the DATA= option, the procedure uses the most recently created SAS data set.

MISSING

treats missing values as a valid (nonmissing) category for all categorical variables, which include TABLES, STRATA, and CLUSTER variables.

By default (if you do not specify the MISSING option), PROC SURVEYFREQ excludes an observation from the analysis if the observation contains a missing value for any STRATA or CLUSTER variable. By default, PROC SURVEYFREQ also excludes an observation from the analysis if the observation contains a missing value for any variable in the table request. For more information, see the section Missing Values.

NOMCAR

includes observations with missing values of TABLES variables in the variance computation as not missing completely at random (NOMCAR) for Taylor series variance estimation. When you specify the NOMCAR option, PROC SURVEYFREQ computes variance estimates by analyzing the nonmissing values as a domain (subpopulation), where the entire population includes both nonmissing and missing domains. For more information, see the section Missing Values.

By default, PROC SURVEYFREQ completely excludes an observation from a frequency or crosstabulation table (and the corresponding variance computations) if that observation has a missing value for any of the variables in the table request, unless you specify the MISSING option. The NOMCAR option has no effect when you specify the MISSING option, which treats missing values as a valid nonmissing level.

The NOMCAR option applies only to Taylor series variance estimation; it does not apply to replication variance estimation methods.

NOSUMMARY

suppresses the display of the "Data Summary" table, which PROC SURVEYFREQ produces by default. For information about this table, see the section Data Summary Table.

ORDER=DATA | FORMATTED | FREQ | INTERNAL

specifies the order of the variable levels in the frequency and crosstabulation tables, which you request in the TABLES statement. The ORDER= option also controls the order of the STRATA variable levels in the "Stratum Information" table.

The ORDER= option can take the following values:

ORDER=	Levels Ordered 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
INTERNAL	Unformatted value

By default, ORDER=INTERNAL. The FORMATTED and INTERNAL orders are machine-dependent. The frequency count used by ORDER=FREQ is the nonweighted frequency (sample size), rather than the weighted frequency.

For more information about sort order, see the chapter on the SORT procedure in the Base SAS Procedures Guide and the discussion of BY-group processing in SAS Language Reference: Concepts.

PAGE

displays only one table per page. Otherwise, PROC SURVEYFREQ displays multiple tables per page as space permits.

RATE=value | SAS-data-set R=value | SAS-data-set

specifies the sampling rate, which PROC SURVEYFREQ uses to compute a finite population correction for Taylor series variance estimation. This option is ignored for replication variance estimation methods.

If your sample design has multiple stages, you should specify the first-stage sampling rate, which is the ratio of the number of primary sampling units (PSUs) in the sample to the total number of PSUs in the population.

You can specify the sampling rate in either of the following ways:

value: specifies a nonnegative number to use for a nonstratified design or for a stratified design that has the same sampling rate in each stratum.
SAS-data-set: specifies a SAS-data-set that contains the stratification variables and the sampling rates for a stratified design that has different sampling rates in the strata. You must provide the sampling rates in the data set variable named _RATE_. The sampling rates must be nonnegative numbers.

You can specify sampling rates as numbers between 0 and 1. Or you can specify sampling rates in percentage form as numbers between 1 and 100, which PROC SURVEYFREQ converts to proportions. The procedure treats the value 1 as 100% instead of 1%.

For more information, see the section Population Totals and Sampling Rates.

If you do not specify either the RATE= or the TOTAL= option, the Taylor series variance estimation does not include a finite population correction. You cannot specify both the RATE= and TOTAL= options.

TOTAL=value | SAS-data-set N=value | SAS-data-set

specifies the total number of primary sampling units (PSUs) in the study population. PROC SURVEYFREQ uses this information to compute a finite population correction for Taylor series variance estimation. This option is ignored for replication variance estimation methods.

You can specify the total number of PSUs in either of the following ways:

value: specifies a positive number to use for a nonstratified design or for a stratified design that has the same population total in each stratum.
SAS-data-set: specifies a SAS-data-set that contains the stratification variables and the population totals for a stratified design that has different population totals in the strata. You must provide the stratum totals in the data set variable named _TOTAL_. The stratum totals must be positive numbers.

For more information, see the section Population Totals and Sampling Rates.

If you do not specify either the TOTAL= or the RATE= option, the Taylor series variance estimation does not include a finite population correction. You cannot specify both the TOTAL= and RATE= options.

VARHEADER=LABEL | NAME | NAMELABEL

specifies the variable identification to use in the displayed output. This option controls the headings of the variable columns in one-way frequency tables, crosstabulation tables, and the "Stratum Information" table. This option also controls the variable identification in table titles. By default, VARHEADER=NAME.

The VARHEADER= option can take the following values:

VARHEADER=	Variable Identification Displayed
LABEL	Variable label
NAME	Variable name
NAMELABEL	Variable name and label, as Name (Label)

VARMETHOD=method <(method-options)>

specifies the variance estimation method. PROC SURVEYFREQ provides the Taylor series method and the following replication (resampling) methods: balanced repeated replication (BRR), jackknife, and bootstrap.

Table 111.2 summarizes the available methods and method-options.

Table 111.2: Variance Estimation Methods

method	Variance Estimation Method	method-options
BOOTSTRAP	Bootstrap	None
BRR	Balanced repeated replication	DFADJ
		FAY <=value>
		HADAMARD=SAS-data-set
		OUTWEIGHTS=SAS-data-set
		PRINTH
		REPS=number
JACKKNIFE \| JK	Jackknife	DFADJ
		OUTJKCOEFS=SAS-data-set
		OUTWEIGHTS=SAS-data-set
TAYLOR	Taylor series linearization	None

For VARMETHOD=BRR and VARMETHOD=JACKKNIFE, you can specify method-options in parentheses after the variance method name. For example:

varmethod=BRR(reps=60 outweights=myReplicateWeights)

By default, VARMETHOD=JACKKNIFE if you also specify a REPWEIGHTS statement; otherwise, VARMETHOD=TAYLOR by default.

You can specify the following methods:

BOOTSTRAP

requests bootstrap variance estimation. When you specify this option, you must also provide bootstrap replicate weights by using the REPWEIGHTS statement; PROC SURVEYFREQ does not create bootstrap weights. For more information, see the section Bootstrap.

BRR <(method-options)>

requests variance estimation by balanced repeated replication (BRR). This method requires a stratified sample design where each stratum contains two primary sampling units (PSUs). When you specify this method, you must also specify a STRATA statement unless you provide replicate weights by using the REPWEIGHTS statement. For more information, see the section Balanced Repeated Replication (BRR).

You can specify the following method-options:

DFADJ

computes the degrees of freedom as the number of nonmissing strata for the individual table request. If you specify this option, PROC SURVEYFREQ does not count any empty strata that occur when observations that have missing values of the TABLES variables are removed from the analysis of the table. By default, PROC SURVEYFREQ computes the degrees of freedom by counting the number of nonmissing strata for all valid observations in the input data set.

For more information, see the section Degrees of Freedom. For information about valid observations, see the section Data Summary Table.

This method-option has no effect when you specify the MISSING option, which treats missing values as a valid nonmissing level.

This method-option is not used when you specify the degrees of freedom in the DF= option in the TABLES statement or when you specify a REPWEIGHTS statement to provide replicate weights. When you specify a REPWEIGHTS statement, the degrees of freedom are the number of REPWEIGHTS variables (replicates) unless you specify the DF= option in the REPWEIGHTS or the TABLES statement.

FAY <=value>

requests Fay’s method, which is a modification of the BRR method. For more information, see the section Fay’s BRR.

You can specify the value of the Fay coefficient, which is used in converting the original sampling weights to replicate weights. The Fay coefficient must be a nonnegative number less than 1. By default, the Fay coefficient is 0.5.

HADAMARD=SAS-data-set H=SAS-data-set

names a SAS-data-set that contains the Hadamard matrix for BRR replicate construction. If you do not specify this method-option, PROC SURVEYFREQ generates an appropriate Hadamard matrix for replicate construction. For more information, see the sections Balanced Repeated Replication (BRR) and Hadamard Matrix.

If a Hadamard matrix of a particular dimension exists, it is not necessarily unique. Therefore, if you want to use a specific Hadamard matrix, you must provide the matrix as a SAS-data-set in this method-option.

In the HADAMARD= input data set, each variable corresponds to a column and each observation corresponds to a row of the Hadamard matrix. You can use any variable names in the HADAMARD= data set. All values in the data set must equal either 1 or –1. You must ensure that the matrix you provide is indeed a Hadamard matrix—that is, , where is the Hadamard matrix of dimension R and is an identity matrix. PROC SURVEYFREQ does not check the validity of the Hadamard matrix that you provide.

The HADAMARD= input data set must contain at least H variables, where H denotes the number of first-stage strata in your design. If the data set contains more than H variables, PROC SURVEYFREQ uses only the first H variables. Similarly, the HADAMARD= input data set must contain at least H observations.

If you do not specify the REPS= method-option, the number of replicates is assumed to be the number of observations in the HADAMARD= input data set. If you specify the number of replicates—for example, REPS=nreps—the first nreps observations in the HADAMARD= data set are used to construct the replicates.

You can specify the PRINTH method-option to display the Hadamard matrix that PROC SURVEYFREQ uses to construct replicates for BRR.

OUTWEIGHTS=SAS-data-set

names a SAS-data-set to store the replicate weights that PROC SURVEYFREQ creates for BRR variance estimation. For information about replicate weights, see the section Balanced Repeated Replication (BRR). For information about the contents of the OUTWEIGHTS= data set, see the section Replicate Weight Output Data Set.

The OUTWEIGHTS= method-option is not available when you provide replicate weights in a REPWEIGHTS statement.

PRINTH

displays the Hadamard matrix that PROC SURVEYFREQ uses to construct replicates for BRR variance estimation. When you provide the Hadamard matrix in the HADAMARD= method-option, PROC SURVEYFREQ displays only the rows and columns that are actually used to construct replicates. For more information, see the sections Balanced Repeated Replication (BRR) and Hadamard Matrix.

The PRINTH method-option is not available when you provide replicate weights in a REPWEIGHTS statement because the procedure does not use a Hadamard matrix in this case.

REPS=number

specifies the number of replicates for BRR variance estimation. The value of number must be an integer greater than 1.

If you do not use the HADAMARD= method-option to provide a Hadamard matrix, the number of replicates should be greater than the number of strata and should be a multiple of 4. For more information, see the section Balanced Repeated Replication (BRR). If PROC SURVEYFREQ cannot construct a Hadamard matrix for the REPS= value that you specify, the value is increased until a Hadamard matrix of that dimension can be constructed. Therefore, the actual number of replicates that PROC SURVEYFREQ uses might be larger than number.

If you use the HADAMARD= method-option to provide a Hadamard matrix, the value of number must not be greater than the number of rows in the Hadamard matrix. If you provide a Hadamard matrix and do not specify the REPS= method-option, the number of replicates is the number of rows in the Hadamard matrix.

If you do not specify the REPS= or the HADAMARD= method-option and do not use a REPWEIGHTS statement, the number of replicates is the smallest multiple of 4 that is greater than the number of strata.

If you use a REPWEIGHTS statement to provide replicate weights, PROC SURVEYFREQ does not use the REPS= method-option; the number of replicates is the number of REPWEIGHTS variables.

JACKKNIFE <(method-options)> JK <(method-options)>

requests variance estimation by the delete-1 jackknife method. For more information, see the section Jackknife. If you use a REPWEIGHTS statement to provide replicate weights, VARMETHOD=JACKKNIFE is the default variance estimation method.

The delete-1 jackknife method requires at least two primary sampling units (PSUs) in each stratum for stratified designs unless you use a REPWEIGHTS statement to provide replicate weights.

You can specify the following method-options:

DFADJ

computes the degrees of freedom by using the number of nonmissing strata and clusters for the individual table request. If you specify this method-option, PROC SURVEYFREQ does not count any empty strata or clusters that occur when observations that have missing values of the TABLES variables are removed from the analysis of the table. By default, PROC SURVEYFREQ computes the degrees of freedom by counting the number of nonmissing strata and clusters for all valid observations in the input data set. The degrees of freedom for VARMETHOD=JACKKNIFE equal the number of clusters minus the number of strata.

For more information, see the section Degrees of Freedom. For information about valid observations, see the section Data Summary Table.

This method-option has no effect when you specify the MISSING option, which treats missing values as a valid nonmissing level.

OUTJKCOEFS=SAS-data-set

names a SAS-data-set to store the jackknife coefficients. For information about jackknife coefficients, see the section Jackknife. For information about the contents of the OUTJKCOEFS= data set, see the section Jackknife Coefficient Output Data Set.

OUTWEIGHTS=SAS-data-set

names a SAS-data-set to store the replicate weights that PROC SURVEYFREQ creates for jackknife variance estimation. For information about replicate weights, see the section Jackknife. For information about the contents of the OUTWEIGHTS= data set, see the section Replicate Weight Output Data Set.

This method-option is not available when you use a REPWEIGHTS statement to provide replicate weights.

TAYLOR

requests Taylor series variance estimation. This is the default method if you do not specify the VARMETHOD= option or a REPWEIGHTS statement. For more information, see the section Taylor Series Variance Estimation.