pdf("rpd07_01r.pdf") alldata <- matrix( c(1,676,33,5,1441.67,35184.5,16.4524, 2,516,35,4.75,1299.19,28170.4,13.9852, 3,1052,32,4.2,1154.27,26455,15.3276, 4,868,30,4.4,1045.15,25072.9,17.3128, 5,1008,33,5.55,521.62,31664.2,22.3312, 6,436,33,5.05,1273.02,25491.7,12.2778, 7,544,36,4.25,1346.35,20877.3,17.8225, 8,680,30,4.45,1253.88,25621.3,14.3516, 9,640,38,4.75,1242.65,27587.3,13.6826, 10,492,30,4.6,1281.95,26511.7,11.7566, 11,984,30,4.1,553.69,7886.5,9.882, 12,1400,37,3.45,494.74,14596,16.6752, 13,1276,33,3.45,525.97,9826.8,12.373, 14,1736,36,4.1,571.14,11978.4,9.4058, 15,1004,30,3.5,408.64,10368.6,14.9302, 16,396,30,3.25,646.65,17307.4,31.2865, 17,352,27,3.35,514.03,12822,30.1652, 18,328,29,3.2,350.73,8582.6,28.5901, 19,392,34,3.35,496.29,12369.5,19.8795, 20,236,36,3.3,580.92,14731.9,18.5056, 21,392,30,3.25,535.82,15060.6,22.1344, 22,268,28,3.25,490.34,11056.3,28.6101, 23,252,31,3.2,552.39,8118.9,23.1908, 24,236,31,3.2,661.32,13009.5,24.6917, 25,340,35,3.35,672.15,15003.7,22.6758, 26,2436,29,7.1,528.65,10225,0.3729, 27,2216,35,7.35,563.13,8024.2,0.2703, 28,2096,35,7.45,497.96,10393,0.3205, 29,1660,30,7.45,458.38,8711.6,0.2648, 30,2272,30,7.4,498.25,10239.6,0.2105, 31,824,26,4.85,936.26,20436,18.9875, 32,1196,29,4.6,894.79,12519.9,20.9687, 33,1960,25,5.2,941.36,18979,23.9841, 34,2080,26,4.75,1038.79,22986.1,19.9727, 35,1764,26,5.2,898.05,11704.5,21.3864, 36,412,25,4.55,989.87,17721,23.7063, 37,416,26,3.95,951.28,16485.2,30.5589, 38,504,26,3.7,939.83,17101.3,26.8415, 39,492,27,3.75,925.42,17849,27.7292, 40,636,27,4.15,954.11,16949.6,21.5699, 41,1756,24,5.6,720.72,11344.6,19.6531, 42,1232,27,5.35,782.09,14752.4,20.3295, 43,1400,26,5.5,773.3,13649.8,19.588, 44,1620,28,5.5,829.26,14533,20.1328, 45,1560,28,5.4,856.96,16892.2,19.242),byrow=T,ncol=7) bio <- alldata[,2] sal <- alldata[,3] ph <- alldata[,4] k <- alldata[,5] na <- alldata[,6] zn <- alldata[,7] linth5 <- data.frame(bio,sal,ph,k,na,zn) attach(linth5) model1 <- lm(bio ~ sal+ph+k+na+zn) summary(model1) model2 <- step(model1) summary(model2) library(leaps) allpossreg <- regsubsets(bio ~ sal+ph+k+na+zn,nbest=5,data=linth5) aprout <- summary(allpossreg) with(aprout,round(cbind(which,rsq,adjr2,cp,bic),3)) # These Stepwise Methods are based on Model Criteria, not individual regression coefficients # direction="both" begins like backward and works down # Criteria: k=2 uses AIC (default) k=log(length(y)) uses BIC reg.full <- lm(bio ~ sal+ph+k+na+zn) reg.null <- lm(bio ~ 1) summary(reg.full) forward.reg <- step(reg.null,direction="forward",scope=list(upper=reg.full,lower=reg.null)) summary(forward.reg) backward.reg <- step(reg.full,direction="backward",k=log(length(bio))) summary(backward.reg) stepwise.reg <- step(reg.full,direction="both") summary(stepwise.reg) dev.off()