Centre for Excellence in Teaching and Learning (CETL)

RLO: Descriptive statistics for interval and ratio scale data

Measures of dispersion

Whilst the values of the mean, mode and median may be useful in telling us something about how similar individual interval or ratio scale data values are to one another, they do not help us to understand how different the data values are from one another. There are two measures that are commonly used. These are range and standard deviation.

The range: This is a frequently report measure. It is simply the difference between the lowest value and the highest value. Thus in our 'street' the youngest person may be 2 years old, and the eldest is 98 years old. This shows us that there is a spread of age or range of 96 years. In a street in the student quarter of town it could be very different, with the youngest being 17 years old and the eldest being 35 years. Thus being able to see the range of values helps us to appreciate what the limits of our data range are.

Previous Next