Annual rainfall in Samaru

Drag the horizontal red line and explain that the 'percentiles' jump between data points when read off the cumulative distn function.

Click Smooth function to display a smoothed version of the cdf and show that the 'percentiles' read off it change much more smoothly. The values for the percentiles given by computer software can be thought of as being read off a similar smoothed cdf.

Use the pop-up menu at the top of the diagram to display the full rainfall data set. With larger data sets, there is less difference between the step function and its smooth version.

This is the same data as described in the first page of the section — annual rainfal in Samaru from 1928 to 1983. (The first data set is a subset of this.)