**Normal distribution **

The normal distribution curve is often referred to as a Bell curve or a Gaussian curve. Gauss was a German mathematician in the nineteenth century.

It shows probability information about a population of data, for example, the size of books published in one year or the height of people in a country.

Once all the data was measured you could calculate mean height.

Most of the data will be clustered about this mean value.

The details are that 2/3 of the population would be between minus one Standard Deviation from the mean and one standard deviation of the mean. That is a band 2 SDs wide about the mean. That band would represent most people.

Very few people would be 3 or 4 SD away from the mean, representing the very short and tall people.

The standard deviation is a measure of how widely distributed the data is; a bigger deviation means information is more spread out than one of a smaller standard deviation.

But regardless of the value of the SD, the shape of the curve would be the same.