**[SVY] svy** -- The survey prefix command

__Syntax__

**svy** [*vcetype*] [**,** * svy_options* *eform_option*] **:** *command*

*vcetype* Description
-------------------------------------------------------------------------
SE
__linear__**ized** Taylor-linearized variance estimation
**bootstrap** bootstrap variance estimation; see **[SVY] svy**
**bootstrap**
**brr** BRR variance estimation; see **[SVY] svy brr**
__jack__**knife** jackknife variance estimation; see **[SVY] svy**
**jackknife**
**sdr** SDR variance estimation; see **[SVY] svy sdr**
-------------------------------------------------------------------------
Specifying a *vcetype* overrides the default from **svyset**.

*svy_options* Description
-------------------------------------------------------------------------
if/in
__sub__**pop(**[*varname*] [*if*]**)** identify a subpopulation

SE
**dof(***#***)** design degrees of freedom
*bootstrap_options* more options allowed with bootstrap variance
estimation
*brr_options* more options allowed with BRR variance
estimation
*jackknife_options* more options allowed with jackknife variance
estimation
*sdr_options* more options allowed with SDR variance
estimation

Reporting
__l__**evel(***#***)** set confidence level; default is **level(95)**
__nocnsr__**eport** do not display constraints
*display_options* control columns and column formats, row spacing,
line width, display of omitted variables and
base and empty cells, and factor-variable
labeling

__noh__**eader** suppress table header
__nol__**egend** suppress table legend
__noadj__**ust** do not adjust model Wald statistic
__noi__**sily** display any output from *command*
__tr__**ace** trace *command*
__coefl__**egend** display legend instead of statistics
-------------------------------------------------------------------------
**svy** requires that the survey design variables be identified using **svyset**.
*command* defines the estimation command to be executed. The **by** prefix
cannot be part of *command*.
**mi estimate** may be used with **svy linearized** if the estimation command
allows **mi estimate**; it may not be used with **svy bootstrap**, **svy brr**, **svy**
**jackknife**, or **svy sdr**.
**noheader**, **nolegend**, **noadjust**, **noisily**, **trace**, and **coeflegend** are not
shown in the dialog boxes for estimation commands.
Warning: Using **if** or **in** restrictions will often not produce correct
variance estimates for subpopulations. To compute estimates for
subpopulations, use the **subpop()** option.
See **[SVY] svy postestimation** for features available after estimation.

__Description__

**svy** fits statistical models for complex survey data by adjusting the
results of a command for survey settings identified by **svyset**. Any Stata
estimation command listed in **[SVY] svy estimation** may be used with **svy**.
User-written programs that meet the requirements in **[P] program**
**properties** may also be used.

__Options__

+-------+
----+ if/in +------------------------------------------------------------

**subpop(***subpop***)** specifies that estimates be computed for the single
subpopulation identified by *subpop*, which is

[*varname*] [*if*]

Thus the subpopulation is defined by the observations for which
*varname*!=0 that also meet the **if** conditions. Typically, *varname*=1
defines the subpopulation, and *varname*=0 indicates observations not
belonging to the subpopulation. For observations whose subpopulation
status is uncertain, *varname* should be set to a missing value; such
observations are dropped from the estimation sample.

See **[SVY] subpopulation estimation** and **[SVY] estat**.

+----+
----+ SE +---------------------------------------------------------------

**dof(***#***)** specifies the design degrees of freedom, overriding the default
calculation, df = N_psu - N_strata.

*bootstrap_options* are other options that are allowed with bootstrap
variance estimation specified by **svy** **bootstrap** or specified as **svyset**
using the **vce(bootstrap)** option; see **[SVY]** *bootstrap_options*.

*brr_options* are other options that are allowed with BRR variance
estimation specified by **svy** **brr** or specified as **svyset** using the
**vce(brr)** option; see **[SVY]** *brr_options*.

*jackknife_options* are other options that are allowed with jackknife
variance estimation specified by **svy** **jackknife** or specified as **svyset**
using the **vce(jackknife)** option; see **[SVY]** *jackknife_options*.

*sdr_options* are other options that are allowed with SDR variance
estimation specified by **svy** **sdr** or specified as **svyset** using the
**vce(sdr)** option; see **[SVY]** *sdr_options*.

+-----------+
----+ Reporting +--------------------------------------------------------

**level(***#***)** specifies the confidence level, as a percentage, for confidence
intervals. The default is **level(95)** or as set by **set level**.

**nocnsreport**; see **[R] estimation options**.

*display_options*: **noci**, __nopv__**alues**, __noomit__**ted**, **vsquish**, __noempty__**cells**,
__base__**levels**, __allbase__**levels**, __nofvlab__**el**, **fvwrap(***#***)**, **fvwrapon(***style***)**,
**cformat(***%fmt***)**, **pformat(%***fmt***)**, **sformat(%***fmt***)**, and **nolstretch**; see **[R]**
**estimation options**.

The following options are available with **svy** but are not shown in the
dialog boxes:

**noheader** prevents the table header from being displayed. This option
implies **nolegend**.

**nolegend** prevents the table legend identifying the subpopulations from
being displayed.

**noadjust** specifies that the model Wald test be carried out as *W*/*k*
distributed *F*(*k*,*d*), where *W* is the Wald test statistic, *k* is the
number of terms in the model excluding the constant term, *d* is the
total number of sampled PSUs minus the total number of strata, and
*F*(*k*,*d*) is an *F* distribution with *k* numerator degrees of freedom and *d*
denominator degrees of freedom. By default, an adjusted Wald test is
conducted: (*d*-*k*+1)*W*/(*kd*) distributed *F*(*k*,*d*-*k*+*1*).

See Korn and Graubard (1990) for a discussion of the Wald test and
the adjustments thereof. Using the **noadjust** option is not
recommended.

**noisily** requests that any output from *command* be displayed.

**trace** causes a trace of the execution of *command* to be displayed.

**coeflegend**; see **[R] estimation options**.

The following option is usually available with **svy** at the time of
estimation or on replay but is not shown in all dialog boxes:

*eform_option*; see **[R]** *eform_option*.

__Examples__

**. webuse nhanes2f**
**. svyset psuid [pweight=finalwgt], strata(stratid)**
**. svy: mean zinc**
**. mean zinc**

**. svyset [pweight=finalwgt]**
**. svy: mean zinc**

**. svyset psuid [pweight=finalwgt]**
**. svy: mean zinc**

**. svyset psuid [pweight=finalwgt], strata(stratid)**
**. svy: regress zinc age age2 weight female black orace rural**

__Stored results__

**svy** stores the following in **e()**:

Scalars
**e(N)** number of observations
**e(N_sub)** subpopulation observations
**e(N_strata)** number of strata
**e(N_strata_omit)** number of strata omitted
**e(singleton)** **1** if singleton strata, **0** otherwise
**e(census)** **1** if census data, **0** otherwise
**e(F)** model F statistic
**e(df_m)** model degrees of freedom
**e(df_r)** variance degrees of freedom
**e(N_pop)** estimate of population size
**e(N_subpop)** estimate of subpopulation size
**e(N_psu)** number of sampled PSUs
**e(stages)** number of sampling stages
**e(k_eq)** number of equations in **e(b)**
**e(k_aux)** number of ancillary parameters
**e(p)** p-value
**e(rank)** rank of **e(V)**

Macros
**e(prefix)** **svy**
**e(cmdname)** command name from *command*
**e(cmd)** same as **e(cmdname)** or **e(vce)**
**e(command)** *command*
**e(cmdline)** command as typed
**e(wtype)** weight type
**e(wexp)** weight expression
**e(weight***#***)** variable identifying weight for stage *#*
**e(wvar)** weight variable name
**e(singleunit)** **singleunit()** setting
**e(strata)** **strata()** variable
**e(strata***#***)** variable identifying strata for stage *#*
**e(psu)** **psu()** variable
**e(su***#***)** variable identifying sampling units for stage *#*
**e(fpc)** **fpc()** variable
**e(fpc***#***)** FPC for stage *#*
**e(title)** title in estimation output
**e(poststrata)** **poststrata()** variable
**e(postweight)** **postweight()** variable
**e(vce)** *vcetype* specified in **vce()**
**e(vcetype)** title used to label Std. Err.
**e(mse)** **mse**, if specified
**e(subpop)** *subpop* from **subpop()**
**e(adjust)** **noadjust**, if specified
**e(properties)** **b V**
**e(estat_cmd)** program used to implement **estat**
**e(predict)** program used to implement **predict**
**e(marginsnotok)** predictions disallowed by **margins**
**e(marginswtype)** weight type for **margins**

Matrices
**e(b)** estimates
**e(V)** design-based variance
**e(V_srs)** simple-random-sampling-without-replacement
variance, V_srswor hat
**e(V_srssub)** subpopulation
simple-random-sampling-without-replacement
variance, V_srswor hat (created only when
**subpop()** is specified)
**e(V_srswr)** simple-random-sampling-with-replacement variance,
V_srswr hat (created only when **fpc()** option is
**svyset**)
**e(V_srssubwr)** subpopulation
simple-random-sampling-with-replacement
variance, V_srswr hat (created only when
**subpop()** is specified)
**e(V_modelbased)** model-based variance
**e(V_msp)** variance from misspecified model fit, V_msp hat
**e(_N_strata_single)** number of strata with one sampling unit
**e(_N_strata_certain)** number of certainty strata
**e(_N_strata)** number of strata

Functions
**e(sample)** marks estimation sample

**svy** also carries forward most of the results already in **e()** from *command*.

__Reference__

Korn, E. L., and B. I. Graubard. 1990. Simultaneous testing of
regression coefficients with complex survey data: Use of Bonferroni t
statistics. *American Statistician* 44: 270-276.