Central tendency suitability

Lesson

There are three measures of central tendency that you will need to consider - mean, median and mode.

When deciding which to use you need to remember that the whole data set should be represented by whichever measure you choose. There are two main things you should look out for. The first is a repeated value. If the same data point keeps coming up, it is probably a good representation of the whole data set. This would suggest the mode is the best measure of centre to use.

The second thing you should look out for is an outlier. An outlier is something that is very different to the rest of the data set. For example, if you went to a shop to buy a chocolate bar and found most were around $\$1$$1 but there was one bar that cost $\$20$$20 the expensive bar is an outlier.

So which measure of centre do you choose? The decision tree below should help.

Worked Examples

QUESTION 1

A set of data has a mean of $x$x, the outlier is removed and the mean rises. The outlier must have had:

a value, but we cannot tell if it was larger or smaller
A
a value smaller than the values that remain
B
a value larger than the values that remain
C

QUESTION 2

A set of data has a mean of $x$x, the outlier is removed and the median lowers. The outlier must have had:

a value smaller than the values that remain
A
a value, but we cannot tell if it was larger or smaller
B
a value larger than the values that remain
C

QUESTION 3

The number of $animal$ races that were won by a trainer over the years shown are listed in the table.

Year	$2003$2003	$2004$2004	$2005$2005	$2006$2006	$2007$2007
Races won	$116$116	$105$105	$102$102	$108$108	$113$113

What measure of centre should you use for the data above?
Mean
A
Median
B

Outcomes

11C.D.1.8

Explain the appropriate use of measures of central tendency and measures of spread