Rforch08 - R Material for Chapter 08 >...

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R Material for Chapter 08 > attach(concent.data) > concent.data time concent 1 6 0.0290 2 6 0.0350 3 6 0.0220 4 8 0.0790 5 8 0.0650 6 8 0.0880 7 10 0.1810 8 10 0.1620 9 10 0.2040 10 12 0.4250 11 12 0.3820 12 12 0.4720 13 14 1.1630 14 14 1.0810 15 14 1.2450 16 16 2.8420 17 16 2.4680 18 16 3.0997 > mtime <- mean(time) > mtime [1] 11 > ctime <- time - mtime ## centering the variable time at its mean > ctime [1] -5 -5 -5 -3 -3 -3 -1 -1 -1 1 1 1 3 3 3 5 5 5 > sqctime <- ctime*ctime > cuctime <- ctime*sqctime > fctime <- sqctime*sqctime > reg1 <- lm(concent ~ time) ## simple linear model of time alone > summary(reg1) Call: lm(formula = concent ~ time) Residuals: Min 1Q Median 3Q Max -0.6463 -0.3679 -0.1251 0.4738 1.0786 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) -1.95002 0.42739 -4.563 0.000319 *** time 0.24820 0.03711 6.689 5.2e-06 *** --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 0.5377 on 16 degrees of freedom Multiple R-squared: 0.7366, Adjusted R-squared: 0.7201 F-statistic: 44.74 on 1 and 16 DF, p-value: 5.203e-06 > reg2 <- lm(concent ~ ctime + sqctime) ## model using centered time and square of ## centered time > summary(reg2) Call: lm(formula = concent ~ ctime + sqctime) Residuals: Min 1Q Median 3Q Max -0.31893 -0.14562 -0.08059 0.16476 0.45448
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Rforch08 - R Material for Chapter 08 &gt;...

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