Two tailed normal curve completely labeled

General
1

I am trying to generate a normal curve centered at 95 with Standard deviation 2. This normal curve needs to have 2 blue 2.5% of area under the curve and one region where 95% of the area is in the middle and red. I am trying to do this using only variables but cannot mentally go any further with what is available online. Please help me finish this code as much as possible.

leftxlim = 60
rightxlim = 130
mean = 95
SD = 2
#Two tailed test plotting
bt<-seq(leftxlim ,rightxlim,1)
plot(bt,dnorm(bt,mean,SD),type="l",main="Two tailed test", xlab = "", ylab = "")

abline(v=left.tail.xval)
abline(v=right.tail.xval)

cord.x<-c(leftxlim ,seq(leftxlim,left.tail.xval,1),left.tail.xval)
cord.y<-c(0,dnorm(seq(leftxlim ,left.tail.xval,1),mean,SD),0)
polygon(cord.x,cord.y,col="skyblue")

cord.x1<-c(right.tail.xval,seq(right.tail.xval,rightxlim,1),rightxlim)
cord.y1<-c(0,dnorm(seq(right.tail.xval,rightxlim,1),mean,SD),0)
polygon(cord.x1,cord.y1,col="skyblue")

cord.x2<-c(left.tail.xval,seq(left.tail.xval,right.tail.xval,1),right.tail.xval)
cord.y2<-c(0,dnorm(seq(left.tail.xval,right.tail.xval,1),mean,SD),0)
polygon(cord.x2,cord.y2,col="red")
2

The only lack I see in your code, though I have not checked everything in detail, is the calculation of left.tail.xval and right.tail.xval. These can be calculated with the qnorm() function. For example

left.tail.xval <- qnorm(0.025, 95, 2)
3

excellent i fugred that out but what respect will dnorm be used?

4

Thank you. I was able to resolve this. However is it possible to combine multiple data sets into one plot?

5

To produce two plots on the same image, all you have to do is change the plot function to a lines function when you draw the second distribution. Here is a rather long example.

leftxlim = 60
rightxlim = 130
mean = 95
SD = 2
#Two tailed test plotting
bt<-seq(leftxlim ,rightxlim,1)
plot(bt,dnorm(bt,mean,SD),type="l",main="Two tailed test", xlab = "", ylab = "")

left.tail.xval <- qnorm(0.025, mean, SD)
right.tail.xval <- qnorm(0.975, mean, SD)

abline(v=left.tail.xval)
abline(v=right.tail.xval)

cord.x<-c(leftxlim ,seq(leftxlim,left.tail.xval,1),left.tail.xval)
cord.y<-c(0,dnorm(seq(leftxlim ,left.tail.xval,1),mean,SD),0)
polygon(cord.x,cord.y,col="skyblue")

cord.x1<-c(right.tail.xval,seq(right.tail.xval,rightxlim,1),rightxlim)
cord.y1<-c(0,dnorm(seq(right.tail.xval,rightxlim,1),mean,SD),0)
polygon(cord.x1,cord.y1,col="skyblue")

cord.x2<-c(left.tail.xval,seq(left.tail.xval,right.tail.xval,1),right.tail.xval)
cord.y2<-c(0,dnorm(seq(left.tail.xval,right.tail.xval,1),mean,SD),0)
polygon(cord.x2,cord.y2,col="red")


leftxlim = 60
rightxlim = 130
mean = 85
SD = 2
#Two tailed test plotting
bt<-seq(leftxlim ,rightxlim,1)
lines(bt,dnorm(bt,mean,SD),type="l",main="Two tailed test", xlab = "", ylab = "")

left.tail.xval <- qnorm(0.025, mean, SD)
right.tail.xval <- qnorm(0.975, mean, SD)

abline(v=left.tail.xval)
abline(v=right.tail.xval)

cord.x<-c(leftxlim ,seq(leftxlim,left.tail.xval,1),left.tail.xval)
cord.y<-c(0,dnorm(seq(leftxlim ,left.tail.xval,1),mean,SD),0)
polygon(cord.x,cord.y,col="skyblue")

cord.x1<-c(right.tail.xval,seq(right.tail.xval,rightxlim,1),rightxlim)
cord.y1<-c(0,dnorm(seq(right.tail.xval,rightxlim,1),mean,SD),0)
polygon(cord.x1,cord.y1,col="skyblue")

cord.x2<-c(left.tail.xval,seq(left.tail.xval,right.tail.xval,1),right.tail.xval)
cord.y2<-c(0,dnorm(seq(left.tail.xval,right.tail.xval,1),mean,SD),0)
polygon(cord.x2,cord.y2,col="red")
6

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