Logarithmic Regression: Different correlation from 3 different calculators

06102015, 03:28 PM
(This post was last modified: 06102015 06:30 PM by CR Haeger.)
Post: #12




RE: Logarithmic Regression: Different correlation from 3 different calculators
Thanks  this post made me dig into Minitab and TI36X Pro a bit deeper.
Minitab blog suggests that the standard error, S be used in place of r or r^2 for nonlinear regressions. I believe the formula for S is S = √(Σ(YY')^2/(n2)) where n is number of response Ys and 2 comes from 2 coefficients being "consumed" in the a +b*ln(x) regression. So for your data n2 = 14. Inputting your data into Minitab resulted in S of 8144 (Y units).  TI36X Pro does not seem to offer S up directly but here is a workaround.  Enter and regress the x, y data (in L1, L2) using LNReg  Make sure to store the regression equation into f(x) using RegEQ>f(x): YES  2nd quit to Home screen  In data table, add this formula to L3 column: L3=abs(L2f(L1)) which is absolute residuals. Even after this formula entered, always visit data to refresh L3 after running a regression.  2nd quit to Home screen  Compute 1variable stats on L3. Scroll down to 6:Σ(x^2) = 928584397 which I believe is SSE. MSE would be SSE/14 in this case  Press enter to put Σx^2 onto the home screen  You can build √(Σx^2/14) from this which gives 8144.2 I usually use L3 if I want to compute residuals on any regression. 

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