Statistical terms

Some more statistical terms...

The centre is a value that helps describe the middle or typical or central part of a set of data.

eg Median (an average where you find the middle of an ordered set of data)

eg Mean (an average where you find the sum of all values and divide by how many numbers there are)

The middle 50% is the range of the middle 50% of a set of data. It is the interquartile range.

The Inter-Quartile Range = upper quartile (UQ) - lower quartile (LQ).

It is abbreviated to IQR.

The spread is a value that helps describe the range of a set of data, ie how spread out or close together the data set is. 

eg Range is a measure of spread. Range = highest value - lowest value.

eg IQR is a measure of spread. IQR = UQ - LQ.

eg At higher levels, you will come across the standard deviation. This is also a measure of spread.

An outlier is a value that is quite different to the rest of the data.

eg 2, 4, 4, 6, 7, 9, 11, 12, 12, 13, 15, 39

39 is considered to be an outlier for this set of data.

Example

The data point circled below is likely to be an outlier for this set of data. It has an Engine Size of about 3.3 but has a price of over $80,000, and no over car has a price over $60,000.