```Date: Thu, 29 Oct 1998 14:53:11 GMT Reply-To: Roland Leong Sender: "SPSSX(r) Discussion" From: Roland Leong Organization: Auric, Inc. Subject: Curve estimation Group: I'm a newbie; please forgive my ignorance. I have SPSS Student Version 6.1.3 and the SPSS 6.1 Guide to Data Analysis, which I've read. The book does not cover the use of Statistics-> Regression-> Curve Estimation at all. Is this menu item where you can test how well the data fits the different types of functions. e.g. quadratic and logarithmic, without having to transform the data? I did this with a small set of data, checking off linear and quadratic, and the output was: ======================== Dependent Mth Rsq d.f. F Sigf b0 b1 b2 CONTRIBU LIN .953 8 162.46 .000 7931775 12.1842 CONTRIBU QUA .955 7 74.24 .000 7055649 13.7970 -5.E-07 ======================== Because the R square was slightly higher and the Sigf was small, I guessed that the quadratic would be a better fit. I then transformed my data by adding a variable that was the square of my independent variable and did a stepwise regression with the independent variable and the square of the independent variable. ======================= Multiple R .97625 R Square .95307 Adjusted R Square .94720 Standard Error 2735320.9801 Analysis of Variance DF Sum of Squares Mean Square Regression 1 1215541351209185.00 1215541351209185 Residual 8 59855846914987.6000 7481980864373.45 F = 162.46250 Signif F = .0000 ---------------------- Variables in the Equation ----------------------- Variable B SE B 95% Confdnce Intrvl B Beta FUNDRAIS 12.184219 .955919 9.979868 14.388570 .976252 (Constant) 7931774.9020 1465976.954 4551229.4496 11312320.354 ----------- in ------------ Variable T Sig T FUNDRAIS 12.746 .0000 (Constant) 5.411 .0006 ------------- Variables not in the Equation ------------- Variable Beta In Partial Min Toler T Sig T FUNDSQR -.136406 -.201652 .102565 -.545 .6029 ======================== The answer used only the independent variable and knocked out the independent variable squared. I also ran a linear regression with the independent variable squared =========================== Multiple R .91084 R Square .82964 Adjusted R Square .80834 Standard Error 5211561.9663 Analysis of Variance DF Sum of Squares Mean Square Regression 1 1058114173099310.00 1058114173099310 Residual 8 217283025024862.100 27160378128107.8 F = 38.95801 Signif F = .0002 ---------------------- Variables in the Equation ----------------------- Variable B SE B 95% Confdnce Intrvl B Beta FUNDSQR 3.18204E-06 5.0981E-07 2.00642E-06 4.35767E-06 .910843 (Constant) 15534198.625 2038049.091 10834453.812 20233943.438 ----------- in ------------ Variable T Sig T FUNDSQR 6.242 .0002 (Constant) 7.622 .0001 End Block Number 1 POUT = .100 Limits reached. =========================== QUESTION: Why does the Curve estimation give the indication that a quadratic formula would be the choice, but when I run a quadratic regression it says no go. ```

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