I'm using stepAIC to fit a model. Then I'm trying to use that model to predict future happenings.
My first few variables are labeled as their column. (Is this a problem?) The dataframe that I use to build the model is the same as the data I'm using to predict with. Here is a portion of what is happening.. This is the value it is predicting = > [1] 9.482975 Summary of the model Call: lm(formula = reservesub$paid ~ reservesub[, 3 + i] + reservesub$grads[, i] + reservesub$Sun + reservesub$Fri + reservesub$Sat) Residuals: Min 1Q Median 3Q Max -15.447 -4.993 -1.090 3.910 27.454 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 5.71370 1.46449 3.902 0.000149 *** reservesub[, 3 + i] 1.00868 0.01643 61.391 < 2e-16 *** reservesub$grads[, i] 0.44649 0.12131 3.681 0.000333 *** reservesub$Sun 8.63606 1.95100 4.426 1.93e-05 *** reservesub$Fri 3.76928 2.00079 1.884 0.061682 . reservesub$Sat 4.03103 2.12754 1.895 0.060225 . --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 7.842 on 138 degrees of freedom (131 observations deleted due to missingness) Multiple R-squared: 0.9794, Adjusted R-squared: 0.9787 F-statistic: 1312 on 5 and 138 DF, p-value: < 2.2e-16 Here is the data that is being fed into predicted[p] = predict.(stepsaicguess[[p]], newdata = reservesubpred[p,]) V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15 V16 V17 V18 V19 paid Mon Tue Wed Thu 276 10/3/2010 155 84 76 68 64 63 53 42 42 42 42 38 38 38 35 31 31 NA 84 0 0 0 0 Fri Sat Sun grads.1 grads.2 grads.3 grads.4 grads.5 grads.6 grads.7 0 0 1 8 4 1 10 11 0 0 grads.8 grads.9 grads.10 grads.11 grads.12 grads.13 grads.14 0 4 0 0 3 4 0 In this case, i = 1, so I calculate the predicted value should be 5.7137+1.00868*84+.44649*8+1*8.636+0*3.769+0*4.03=102 But, R is giving me 9.482975 for a predicted value .. (Which, interestingly is 5.7137+3.769*1) (Intercept+Sat) Another question I have is, if I were to include interactions in this model, would I have to make those variables in my prediction dataframe, or would R 'know' what to do? Thanks in advance for your expert assistance. -- View this message in context: http://r.789695.n4.nabble.com/Newb-Prediction-Question-using-stepAIC-and-predict-is-R-wrong-tp3298569p3298569.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.