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help for utest                                                      Version 1.0
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Title

    utest --      Test for U-shaped relationship


Syntax

        utest x f(x) [, options]

    options           Description
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      min(#)          Use # as lower
      max(#)          Use # as upper
      quadratic       Force quadratic specification
      inverse         Force inverse specification
      fieller         Include Fieller-interval of extreme point
      level(#)        set confidence level for Fieller interval; default is
                        level(95)
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Description

    utest provides the exact test of the presence of a U shaped (or inverse U
    shaped) relationship on an interval.

    utest is used after estimation commands to test for the presence of a
    U-shaped or inverse U-shaped relationship between an explanatory variable
    and the outcome variable on a specific interval.

    The estimation must contain the level of the explanatory variable (i.e.
    x) and a non-linear term , either quadratic or inverse (i.e. f(x)). utest
    will determine which of the two is used and report test results from the
    test of the hypothesis that the relationship is decreasing at the start
    of the interval and increasing at the end or vice versa.

    The interval is by default taken as the data range, but can be controlled
    by setting the options minimum(#) and maximum(#).

    A Fieller interval for the extreme point is also provided by the option
    fieller.  This interval is correct even for finite samples.

Remarks

For full details about the test, see Lind and Mehlum: With or Without U? - The 
> appropriate test for a U shaped relationship

Examples

   . utest x xsquared

   . utest x xinv, min(.3) fieller 


 Author

Contact Jo Thori Lind or Halvor Mehlum if you observe problems.


Also see


    Online:  fieller