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From | jl591164@albany.edu |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: interprating orthogonal polynomial regression |
Date | Mon, 26 Jul 2010 12:54:38 -0400 (EDT) |
I used the syntax that Maarten provided to translate the coefficients of the orthogonal polynomials into the original metric of time. The results are below. Then i guess the equation of the cubic mode is represented in the row of deg3, that y=.67-1.46t+.42t²-.03t³. Then what is the formula to get the two reflection points of the curve(the sample mean trajectory showed that there are two reflection points, and it changes directions twice)? Thanks a lot. | deg1 deg2 deg3 _cons -------------+-------------------------------------------- deg1 | -.1405198 0 0 .5339751 deg2 | .5560661 -.0491674 0 -.6281949 deg3 | -1.458612 .4243002 -.0270891 .6659666 _cons | 0 0 0 -.5578475 > *--------------- begin example ---------------- > sysuse auto, clear > orthpoly weight, deg(3) generate(pw*) > logit foreign mpg pw1-pw3 rep78 > orthpoly weight, deg(3) poly(P) > matrix b = e(b) > // extract the polynomials and the constant > matrix b = b[1, "foreign:pw1".."foreign:pw3"], b[1,"foreign:_cons"] > matrix b = b*P > matlist b > > // check > gen w1 = weight > gen w2 = weight^2 > gen w3 = weight^3 > > logit foreign mpg w1-w3 rep78 > *---------------- end example ----------------------- > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/