st: Decreasing returns

["Ronnie Babigumira" <ronnie.babigumira@ios.nlh.no>]

Hi (stata8, win2k, question part stata, part ...). I have a regression

        y = b0 + b1X1 + ..bnXn + e

The coeffcient on X1 is positive but I believe that it exhibits declining
returns. Is there a way (in stata) to test for this (apart from including a
square term for the variable in question).

Ronnie

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