CODEWITHSUNDEEP
rstatisticsnormal-distribution
Hans
Hans

Reputation: 165

Overlaying a histogram with normal distribution

I neeed to draw a histogram of data (weights) overlayed with a line of the expected normal distributioh

I am totally new to R and statistics. I know I probably got something fundamentally wrong about frequencies density and dnorm, but I am stuck.

weights <- c(97.6,95,94.3 ,92.3 ,90.7 ,89.4 ,88.2 ,86.9 ,85.8 ,85.5 ,84.4 ,84.1 ,82.5 ,81.4 ,80.8 ,80  ,79.8 ,79.5 ,78.4 ,78.4 ,78.2 ,78.1 ,78  ,77.4 ,76.5 ,75.4 ,74.8 ,74.1 ,73.5 ,73.2 ,73  ,72.3 ,72.3 ,72.2 ,71.8 ,71.7 ,71.6 ,71.6 ,71.5 ,71.3 ,70.7 ,70.6 ,70.5 ,69.2 ,68.6 ,68.3 ,67.5 ,67  ,66.8 ,66.6 ,65.8 ,65.6 ,64.9 ,64.6 ,64.5 ,64.5 ,64.3 ,64.2 ,63.9 ,63.7 ,62.7 ,62.3 ,62.2 ,59.4 ,57.8 ,57.8 ,57.6 ,56.4 ,53.6 ,53.2 )
hist(weights)
m <- mean(weights)
sd <- sd(weights)
x <- seq(min(weights), max(weights), length.out length(weights))
xn <- dnorm(x, mean = m, sd = sd) * length(weights) #what is the correct factor???
lines(x, xn)

I expected the line to follow the histogram approximately, but it is too low in the histogram

Upvotes: 1

Views: 187

Answers (3)

AkselA
AkselA

Reputation: 8846

You're nearly there, you just have to factor in the histogram bin widths.

weights <- c(97.6, 95, 94.3, 92.3, 90.7, 89.4, 88.2, 86.9, 85.8,
  85.5, 84.4, 84.1, 82.5, 81.4, 80.8, 80, 79.8, 79.5, 78.4, 78.4,
  78.2, 78.1, 78, 77.4, 76.5, 75.4, 74.8, 74.1, 73.5, 73.2, 73,
  72.3, 72.3, 72.2, 71.8, 71.7, 71.6, 71.6, 71.5, 71.3, 70.7,
  70.6, 70.5, 69.2, 68.6, 68.3, 67.5, 67, 66.8, 66.6, 65.8, 65.6,
  64.9, 64.6, 64.5, 64.5, 64.3, 64.2, 63.9, 63.7, 62.7, 62.3,
  62.2, 59.4, 57.8, 57.8, 57.6, 56.4, 53.6, 53.2)

h <- hist(weights, freq=TRUE)
binwi <- diff(h$breaks)[1]

x <- seq(min(weights)-10, max(weights)+10, 0.01)
xn <- dnorm(x, mean=mean(weights), sd=sd(weights)) * length(weights) * binwi
lines(x, xn)

enter image description here

Upvotes: 1

ichisa
ichisa

Reputation: 11

The problem in your code is that hist plots frequencies and dnorm calculates densities. You can try making a histogram with densities and then you will see the histogram or the line just adding freq=F to the histogram: hist(weights, freq = F)

Upvotes: 1

lsfischer
lsfischer

Reputation: 354

what you need is to plot the histogram with the frequency of the examples and then plot the density of the weights, i.e.

weights = c(97.6,95,94.3 ,92.3 ,90.7 ,89.4 ,88.2 ,86.9 ,85.8 ,85.5 ,84.4 ,84.1 ,82.5 ,81.4 ,80.8 ,80  ,79.8 ,79.5 ,78.4 ,78.4 ,78.2 ,78.1 ,78  ,77.4 ,76.5 ,75.4 ,74.8 ,74.1 ,73.5 ,73.2 ,73  ,72.3 ,72.3 ,72.2 ,71.8 ,71.7 ,71.6 ,71.6 ,71.5 ,71.3 ,70.7 ,70.6 ,70.5 ,69.2 ,68.6 ,68.3 ,67.5 ,67  ,66.8 ,66.6 ,65.8 ,65.6 ,64.9 ,64.6 ,64.5 ,64.5 ,64.3 ,64.2 ,63.9 ,63.7 ,62.7 ,62.3 ,62.2 ,59.4 ,57.8 ,57.8 ,57.6 ,56.4 ,53.6 ,53.2 )

hist(weights, prob = T)
lines(density(weights), col = "red")

Hope this helps.

Upvotes: 2

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