Outliers

Skew distributions

Use the top diagram to show how an outlier affects the mean far more than the median. (Drag the highest cross to the right to turn it into an outlier.)

The two data sets that can be displayed in the second diagram are both skew (one with a long tail to the right and the other with a long tail to the left). Explain that the mean is further into the long tail in both cases.

(Note that you can also drag crosses in the second diagram to modify the data.)

The first data set gives the survival times (in days) of 72 guinea pigs that were injected with tubercle bacilli.


Solar cookers are potentially a cheap and environmentally friendly alternative to wood in the developing world. As part of a study of their potential in Botswana, data were collected on the number of sunshine hours in Gaborone. The second data set gives the total sunshine hours on 25th February each year from 1978 to 1997.