= XtSet =

The '''`xtset`''' command declares a panel dataset.

<<TableOfContents>>

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== Usage ==

{{{
. webuse nlswork
(National Longitudinal Survey of Young Women, 14-24 years old in 1968)

. xtset idcode year

Panel variable: idcode (unbalanced)
 Time variable: year, 68 to 88, but with gaps
         Delta: 1 unit
}}}

{{{
. webuse patienttimes

. format tod %tc

. xtset pid tod

Panel variable: pid (unbalanced)
 Time variable: tod, 03dec2005 06:30:00 to 03dec2005 18:00:00, but with gaps
         Delta: .001 seconds
}}}

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== Balanced Data ==

'''Balanced''' and '''unbalanced''' refers to whether each entity has a measurement in each time period. A common issue is misspecifying the time units (e.g., specifying a wave for panel data that had cohorts added and subtracted across waves).

This issue can be 'corrected' using `tsfill` to generate missing values for all gaps. The `full` option will furthermore generate missing values for the leading and trailing 'gaps', i.e. the time periods before and after the entity was actually being measured.

`carryforward` can be used to populate the gaps with the most recent non-missing value.

{{{
webuse nlswork
xtset idcode year
sort id
by id: carryforward birth_yr, generate(birth_yr2)
by id: carryforward birth_yr, replace
}}}

`ipolate` can be used to populate the gaps with interpolated values.

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== Operators ==

See [[Stata/TsSet|tsset]] for the time series operators.



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CategoryRicottone