initial commit

Author: kabacoff

Ch10 Power analysis.R

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+#----------------------------------------#
+# R in Action (2nd ed): Chapter 10       #
+# Power analysis                         #
+# requires packages pwr to be installed  #
+# install.packages("pwr")                #
+#----------------------------------------#
+
+par(ask=TRUE)
+
+library(pwr)
+
+# t tests
+pwr.t.test(d=.8, sig.level=.05,power=.9, type="two.sample",  
+           alternative="two.sided")
+pwr.t.test(n=20, d=.5, sig.level=.01, type="two.sample", 
+           alternative="two.sided")
+
+
+# ANOVA
+pwr.anova.test(k=5,f=.25,sig.level=.05,power=.8)
+
+# Correlations
+pwr.r.test(r=.25, sig.level=.05, power=.90, alternative="greater")
+
+# Linear Models
+pwr.f2.test(u=3, f2=0.0769, sig.level=0.05, power=0.90)
+
+# Tests of proportions
+pwr.2p.test(h=ES.h(.65, .6), sig.level=.05, power=.9, 
+            alternative="greater")
+
+# Chi-square tests
+prob <- matrix(c(.42, .28, .03, .07, .10, .10), byrow=TRUE, nrow=3)
+ES.w2(prob)
+pwr.chisq.test(w=.1853, df=3 , sig.level=.05, power=.9)
+
+
+# Listing 10.1 - Sample sizes for detecting significant effects in a One-Way ANOVA
+es <- seq(.1, .5, .01)
+nes <- length(es)
+samsize <- NULL
+for (i in 1:nes){
+  result <- pwr.anova.test(k=5, f=es[i], sig.level=.05, power=.9)
+  samsize[i] <- ceiling(result$n)
+}
+plot(samsize,es, type="l", lwd=2, col="red",
+     ylab="Effect Size",
+     xlab="Sample Size (per cell)",
+     main="One Way ANOVA with Power=.90 and Alpha=.05")
+
+
+# Listing 10.2 - Sample size curves for dtecting corelations of various sizes
+library(pwr)
+r <- seq(.1,.5,.01)
+nr <- length(r)
+p <- seq(.4,.9,.1)
+np <- length(p)
+samsize <- array(numeric(nr*np), dim=c(nr,np))
+for (i in 1:np){
+  for (j in 1:nr){
+    result <- pwr.r.test(n = NULL, r = r[j],
+                         sig.level = .05, power = p[i],
+                         alternative = "two.sided")
+    samsize[j,i] <- ceiling(result$n)
+  }
+}
+xrange <- range(r)
+yrange <- round(range(samsize))
+colors <- rainbow(length(p))
+plot(xrange, yrange, type="n",
+     xlab="Correlation Coefficient (r)",
+     ylab="Sample Size (n)" )
+for (i in 1:np){
+  lines(r, samsize[,i], type="l", lwd=2, col=colors[i])
+}
+abline(v=0, h=seq(0,yrange[2],50), lty=2, col="grey89")
+abline(h=0, v=seq(xrange[1],xrange[2],.02), lty=2, col="gray89")
+title("Sample Size Estimation for Correlation Studies\n
+Sig=0.05 (Two-tailed)")
+legend("topright", title="Power", as.character(p),
+       fill=colors)
+