Stata 15 help for xtdata

[XT] xtdata -- Faster specification searches with xt data

Syntax

xtdata [varlist] [if] [in] [, options]

options Description ------------------------------------------------------------------------- Main re convert data to a form suitable for random-effects estimation ratio(#) ratio of random effect to pure residual (standard deviations) be convert data to a form suitable for between estimation fe convert data to a form suitable for fixed-effects (within) estimation nodouble keep original variable type; default is to recast type as double clear overwrite current data in memory ------------------------------------------------------------------------- A panel variable must be specified; use xtset.

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Statistics > Longitudinal/panel data > Setup and utilities > Faster specification searches with xt data

Description

xtdata produces a transformed dataset of the variables specified in varlist or of all the variables in the data. Once the data are transformed, Stata's regress command may be used to perform specification searches more quickly than xtreg; see [R] regress and [XT] xtreg. Using xtdata, re also creates a variable named constant. When using regress after xtdata, re, specify noconstant and include constant in the regression. After xtdata, be and xtdata, fe, you need not include constant or specify regress's noconstant option.

Options

+------+ ----+ Main +-------------------------------------------------------------

re specifies that the data be converted into a form suitable for random-effects estimation. re is the default if be, fe, or re is not specified. ratio() must also be specified.

ratio(#) (use with xtdata, re only) specifies the ratio sigma_u/sigma_e, which is the ratio of the random effect to the pure residual. This is the ratio of the standard deviations, not the variances.

be specifies that the data be converted into a form suitable for between estimation.

fe specifies that the data be converted into a form suitable for fixed-effects (within) estimation.

nodouble specifies that transformed variables keep their original types, if possible. The default is to recast variables to double.

Remember that xtdata transforms variables to be differences from group means, pseudodifferences from group means, or group means. Specifying nodouble will decrease the size of the resulting dataset but may introduce roundoff errors in these calculations.

clear specifies that the data may be converted even though the dataset has changed since it was last saved on disk.

Examples

--------------------------------------------------------------------------- Setup . webuse xtdatasmpl

Perform between transformation . xtdata ln_w grade age* ttl_exp* tenure* black not_smsa south, be

Equivalent to xtreg, be . regress ln_w grade age* ttl_exp* tenure* black not_smsa south

--------------------------------------------------------------------------- Setup . webuse xtdatasmpl, clear

Perform within transformation . xtdata, fe

Equivalent to xtreg, fe . regress ln_w grade age* ttl_exp* tenure* black not_smsa south

--------------------------------------------------------------------------- Setup . webuse xtdatasmpl, clear

Perform random-effects transformation . xtdata, re ratio(.88719358)

Equivalent to xtreg, re . regress ln_w grade age* ttl_exp* tenure* black not_smsa south constant, noconstant ---------------------------------------------------------------------------

Warnings

1. xtdata is intended for use during the specification search phase of analysis. Final results should be estimated with xtreg on unconverted data.

2. Using regress after xtdata, fe, produces standard errors that are too small, but only slightly.

3. Interpret significance tests and confidence intervals loosely. After xtdata, fe and re, an incorrect (but close to correct) distribution is being assumed.

4. You should ignore the summary statistics reported at the top of regress's output.

5. After converting the data, you may form linear, but not nonlinear combinations of regressors.


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