Count variables

A count variable counts the number of items or people in a specified time, place, occasion or group. Each observation in a set of count data is a count value. Count data occur in considering situations such as:

• the number of children in a family
• the number of people arriving at a central city railway station in a five-minute interval during peak time
• attendance at football matches
• the number of hits on an internet site per week.

We can see that the first example above of a count variable contrasts with the other examples, in which counts will tend to take many different values. That is, in data on the variables in bullet points 2, 3 and 4 above, repetitions of values of observations are not likely. Also the sizes of the observations will tend to be large, sometimes very large. For these types of count variables the types of graphs and summaries used for continuous variables are often appropriate.