Phillips-Perron test for a unit root                             (STB-17: sts7)
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	^ppunit^ varname [^, l^ags^(^#^) ^t^rend regress_options]


Description
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^ppunit^ tests the null hypothesis that varname has a unit root.  The test is
performed by regressing the first difference of varname on its lagged level.
A time trend may also be included.  The test statistics are derived in Phillips
and Perron.  The Phillips-Perron statistics have the same distribution as the 
Dickey-Fuller statistic.  Type "^help dickey^ for more information.


Options
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^lags(^#^)^ specifies the number of lags to be considered.   The default is 4.

^trend^ includes a time trend term in the regression.

regress_options refers to any of the options of ^regress^; see ^help regress^.


References 
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Fuller, W. A.  1976.  ^Introduction to Statistical Time Series^.  New York:
    John Wiley & Sons.

Phillips, Peter C. B. and Pierre Perron.  1988.  "Testing for a unit root in 
    time series regression," ^Biometrika^.  Vol. 75, pp. 335-46.


Author
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Sean Becketti, Federal Reserve Bank of Kansas City.


Also see
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    STB:  sts2 (STB-7)
On-line:  ^help^ for ^dickey^