Statistics for Maintenance Modelling: Basic Probability Concepts

# The Histogram¤

We have already seen that the expected value (mean) and variance can be used to summarize the essential properties of a random variable. The purpose of a histogram is to graphically summarise the distribution of a univariate data set. The histogram graphically shows the following:

1. center (i.e. the location) of the data
2. spread (i.e. the scale) of the data
3. skewness of the data
4. presence of outliers
5. presence of multiple modes in the data.

These features provide strong indications of the proper distributional model for the data.

This histogram plots a data set containing the width of a specialised drill bit i.e. continuous data. The specifications of the drill bit require that the bit have a diameter between 10.1mm and 10.3mm. Using a histogram, one can immediately see the distribution of the drill bit widths.