Ok.. I see that I did not completely define the polygon. The code below works fine

z <- pretty(c(-3,3), 100)
ht <- dnorm(z)
data <- data.frame(z=z, ht=ht)
zc <- 1.645
plot(data, type="n")
lines(data)
#segments(160,0,160,dnorm(160, m=160, sd=17), lty=2)
t <- subset(data, data$z>zc)
xvals <- t$z
dvals <- t$ht
polygon(c(xvals,rev(xvals)),c(rep(0,length(xvals)),rev(dvals)),col="red")

  ----- Original Message ----- 
  From: LL 
  To: r-help@stat.math.ethz.ch 
  Sent: Saturday, May 26, 2007 12:34 PM
  Subject: polygon error?


  Hi.. I'm not sure why polygon returns an area above the standard normal curve.

  z <- pretty(c(-3,3), 100)
  ht <- dnorm(z)
  data <- data.frame(z=z, ht=ht)
  zc <- 1.645
  plot(data, type="l")
  lines(data)
  t <- subset(data, z>zc)
  polygon(t, col="red")

  Thanks,
  Lance


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