The SURVEYPHREG Procedure

PROC SURVEYPHREG Statement

PROC SURVEYPHREG <options>;

The PROC SURVEYPHREG statement invokes the SURVEYPHREG procedure. It also identifies the data set to be analyzed. Table 113.1 summarizes the options available in the PROC SURVEYPHREG statement.

Table 113.1: PROC SURVEYPHREG Statement Options

Option	Description
DATA=	Names the input SAS data set
MISSING	Treats missing values as a valid category
NOPRINT	Suppresses all displayed output
NOMCAR	Uses missing observations specified as not missing completely at random
ORDER=	Specifies the sort order of CLASS variables
RATE=	Specifies the sampling rate
TOTAL=	Specifies the total number of primary sampling units
VARMETHOD=	Specifies the variance estimation method

You can specify the following options in the PROC SURVEYPHREG statement:

DATA=SAS-data-set

names the SAS data set that contains the data to be analyzed. 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 CLASS, STRATA, CLUSTER, and DOMAIN variables. By default, if you do not specify the MISSING option, an observation is excluded from the analysis if it has a missing value for any of these categorical variables. For more information, see the section Missing Values.

NOPRINT

suppresses all displayed output. Note that this option temporarily disables the Output Delivery System (ODS); see Chapter 20: Using the Output Delivery System, for more information.

NOMCAR

includes observations with missing values of the analysis variables that are specified in the MODEL statement as not missing completely at random (NOMCAR) for Taylor series variance estimation. When you specify the NOMCAR option, PROC SURVEYPHREG computes variance estimates by analyzing the nonmissing values as a domain (subpopulation), where the entire population includes both nonmissing and missing domains. See the section Missing Values for details.

By default, PROC SURVEYPHREG excludes an observation from analyses (and the corresponding variance computations) if that observation has a missing value for any of the variables in the MODEL statement. Note that if you specify the MISSING option for classification variables, then the procedure treats the missing values as a valid nonmissing level.

The NOMCAR option applies only to Taylor series variance estimation. The replication methods, which you request with the VARMETHOD=BRR and VARMETHOD=JACKKNIFE options, do not use the NOMCAR option.

ORDER=DATA | FORMATTED | FREQ | INTERNAL

specifies the sort order for the levels of the classification variables (which are specified in the CLASS statement).

This option applies to the levels for all classification variables, except when you use the (default) ORDER=FORMATTED option with numeric classification variables that have no explicit format. In that case, the levels of such variables are ordered by their internal value.

The ORDER= option can take the following values:

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
INTERNAL	Unformatted value

By default, ORDER=FORMATTED. For ORDER=FORMATTED and ORDER=INTERNAL, the sort order is machine-dependent.

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.

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

specifies the sampling rate as a nonnegative value, or identifies an input data set that gives the stratum sampling rates in a variable named _RATE_. PROC SURVEYPHREG uses this information to compute a finite population correction for Taylor series variance estimation. The procedure does not use the RATE= option for BRR or jackknife variance estimation, which you request with the VARMETHOD=BRR or VARMETHOD=JACKKNIFE option.

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) that are selected to the total number of PSUs in the population.

For a nonstratified sample design, or for a stratified sample design with the same sampling rate in all strata, you should specify a nonnegative value for the RATE= option. If your design is stratified with different sampling rates in different strata, then you should name a SAS data set that contains the stratification variables and the stratum sampling rates. See the section Population Totals and Sampling Rates for details.

The sampling rate value must be a nonnegative number. You can specify value as a number between 0 and 1. Or you can specify value in percentage form as a number between 1 and 100, and PROC SURVEYPHREG converts that number to a proportion. The procedure treats the value 1 as 100% instead of 1%.

If you do not specify the RATE= or TOTAL= option, then the Taylor series variance estimation does not include a finite population correction. You cannot specify both the TOTAL= option and the RATE= option in the same PROC SURVEYPHREG statement.

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

specifies the total number of primary sampling units (PSUs) in the study population as a positive value, or identifies an input data set that gives the stratum population totals in a variable named _TOTAL_. PROC SURVEYPHREG uses this information to compute a finite population correction for Taylor series variance estimation. The procedure does not use the TOTAL= option for BRR or jackknife variance estimation, which you request with the VARMETHOD=BRR or VARMETHOD=JACKKNIFE option.

For a nonstratified sample design, or for a stratified sample design with the same population total in all strata, you should specify a positive value for the TOTAL= option, which refers to the total number of PSUs in each stratum. If your sample design is stratified with different population totals in different strata, then you should name a SAS data set that contains the stratification variables and the stratum totals. See the section Population Totals and Sampling Rates for details.

If you do not specify the TOTAL= or RATE= option, then the Taylor series variance estimation does not include a finite population correction. You cannot specify both the TOTAL= option and the RATE= option in the same PROC SURVEYPHREG statement.

VARMETHOD=BRR < (method-options) > | JACKKNIFE <(method-options) > | TAYLOR

specifies the variance estimation method. VARMETHOD=TAYLOR requests the Taylor series method, which is the default if you do not specify the VARMETHOD= option or a REPWEIGHTS statement. VARMETHOD=BRR requests variance estimation by balanced repeated replication (BRR), and VARMETHOD=JACKKNIFE requests variance estimation by the delete-1 jackknife method.

For VARMETHOD=BRR and VARMETHOD=JACKKNIFE, you can specify method-options in parentheses following the variance method name. Table 113.2 summarizes the available method-options.

Table 113.2: Variance Estimation Options

VARMETHOD=	Variance Estimation Method	Method Options
BRR	Balanced repeated replication	CENTER=FULLSAMPLE \| REPLICATES
		DETAILS
		FAY <=value>
		HADAMARD=SAS-data-set
		OUTWEIGHTS=SAS-data-set
		PRINTH
		REPS=number
JACKKNIFE	Jackknife	CENTER=FULLSAMPLE \| REPLICATES
		DETAILS
		OUTJKCOEFS=SAS-data-set
		OUTWEIGHTS=SAS-data-set
TAYLOR	Taylor series linearization	None

The following values are available for the VARMETHOD= option:

BRR < (method-options) >

requests variance estimation by balanced repeated replication (BRR). The BRR method requires a stratified sample design with two primary sampling units (PSUs) in each stratum. If you specify the VARMETHOD=BRR option, you must also specify a STRATA statement unless you provide replicate weights with a REPWEIGHTS statement. See the section Balanced Repeated Replication (BRR) Method for details.

You can specify the following method-options in parentheses after the VARMETHOD=BRR option:

CENTER=FULLSAMPLE | REPLICATES

defines how to compute the deviations for the BRR method. CENTER=FULLSAMPLE is the default, which computes the deviations of the replicate estimates from the full sample estimate. Alternatively, you can specify CENTER=REPLICATES to compute the deviations of the replicate estimates from the average of the replicate estimates. See the section Balanced Repeated Replication (BRR) Method for details.

DETAILS

displays the maximum likelihood estimates of model parameters for replicate samples when the replicate parameter estimates are available. A replicate sample might not provide useful parameter estimates (replicate estimates), for reasons such as nonconvergence of the optimization or inestimability of some parameters in that replicate sample.

FAY <=value>

requests Fay’s method, which is a modification of the BRR method. See the section Fay’s BRR Method for details.

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 value of the Fay coefficient equals 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 provide a Hadamard matrix with the HADAMARD= method-option, PROC SURVEYPHREG generates an appropriate Hadamard matrix for replicate construction. See the sections Balanced Repeated Replication (BRR) Method and Hadamard Matrix for details.

If a Hadamard matrix of a given 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 the HADAMARD= method-option.

In the HADAMARD= input data set, each variable corresponds to a column of the Hadamard matrix, and each observation corresponds to a row of the 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, $\bA ’\bA = R\bI$ , where $\bA$ is the Hadamard matrix of dimension R and $\bI$ is an identity matrix. PROC SURVEYPHREG 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 SURVEYPHREG 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, then the number of replicates is equal to the number of observations in the HADAMARD= input data set. If you specify the number of replicates—for example, REPS=nreps—then 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 SURVEYPHREG uses to construct replicates for BRR variance estimation.

OUTWEIGHTS=SAS-data-set

names an output SAS data set to store the replicate weights that PROC SURVEYPHREG creates for BRR variance estimation. For more information about replicate weights, see the section Balanced Repeated Replication (BRR) Method. For more information about the contents of the OUTWEIGHTS= data set, see the section Replicate Weights Output Data Set.

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

PRINTH

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

The PRINTH method-option is not available when you provide replicate weights by using a REPWEIGHTS statement, because PROC SURVEYPHREG 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 provide a Hadamard matrix by using the HADAMARD= method-option, 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) Method. If a Hadamard matrix cannot be constructed for the REPS= value that you specify, the value is increased until a Hadamard matrix of that dimension can be constructed. Therefore, it is possible for the actual number of replicates to be larger than the REPS= value that you specify.

If you provide a Hadamard matrix by using the HADAMARD= method-option, the value of REPS= 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 equals the number of rows in the Hadamard matrix.

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

If you provide replicate weights with a REPWEIGHTS statement, the procedure does not use the REPS= method-option. With a REPWEIGHTS statement, the number of replicates equals the number of REPWEIGHTS variables.

JACKKNIFE | JK <(method-options)>

requests variance estimation by the delete-1 jackknife method. See the section Jackknife Method for details. If you provide replicate weights with a REPWEIGHTS statement, VARMETHOD=JACKKNIFE is the default variance estimation method. The JACKKNIFE method requires at least two primary sampling units (PSUs) in each stratum for stratified designs unless you provide replicate weights with a REPWEIGHTS statement.

You can specify the following method-options in parentheses following VARMETHOD=JACKKNIFE:

CENTER=FULLSAMPLE | REPLICATES

defines how to compute the deviations for the jackknife method. CENTER=FULLSAMPLE is the default, which computes the deviations of the replicate estimates from the full sample estimate. Alternatively, you can specify CENTER=REPLICATES to compute the deviations of the replicate estimates from the average of the replicate estimates. See the section Jackknife Method for details.

DETAILS

OUTWEIGHTS=SAS-data-set

names an output SAS data set that contains replicate weights. See the section Jackknife Method for more information about replicate weights. See the section Replicate Weights Output Data Set for more details about the contents of the OUTWEIGHTS= data set.

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

OUTJKCOEFS=SAS-data-set

names an output SAS data set that contains jackknife coefficients . See the section Jackknife Coefficients Output Data Set for more details about the contents of the OUTJKCOEFS= data set.

TAYLOR

requests Taylor series variance estimation. This is the default method if you do not specify the VARMETHOD= option or a REPWEIGHTS statement . See the section Taylor Series Linearization for more information.