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I am using the following code to create a standard normal distribution in R:
x <- seq(-4, 4, length=200) y <- dnorm(x, mean=0, sd=1) plot(x, y, type="l", lwd=2) I need the x-axis to be labeled at the mean and at points three standard deviations above and below the mean. How can I add these labels?
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Properties of a Normal Distribution A normal distribution is bell-shaped and symmetric about its mean. A normal distribution is completely defined by its mean, µ, and standard deviation, σ. The total area under a normal distribution curve equals 1. The x-axis is a horizontal asymptote for a normal distribution curve.
The curve never touches the x axis. Theoretically, no matter how far in either direction the curve extends, it never meets the x axis—but it gets increasingly closer. The total area under a normal distribution curve is equal to 1.00, or 100%.
Figure 9.6: {The normal distribution with mean mu=0 and standard deviation sigma=1. The x-axis corresponds to the value of some variable, and the y-axis tells us something about how likely we are to observe that value. However, notice that the y-axis is labelled “Probability Density” and not “Probability”.
The easiest (but not general) way is to restrict the limits of the x axis. The +/- 1:3 sigma will be labeled as such, and the mean will be labeled as 0 - indicating 0 deviations from the mean.
plot(x,y, type = "l", lwd = 2, xlim = c(-3.5,3.5)) 
Another option is to use more specific labels:
plot(x,y, type = "l", lwd = 2, axes = FALSE, xlab = "", ylab = "") axis(1, at = -3:3, labels = c("-3s", "-2s", "-1s", "mean", "1s", "2s", "3s")) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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