Florence Nightingale's text is in error about the area representation ("If we look at the polar area graph, we can see that the area of each coloured wedge, measured from the centre, is in proportion to the statistic it represents.")

The radius of the wedge is in proportion to the statistic it represents.

Florence Nightingale's text is in error about the area representation ("If we look at the polar area graph, we can see that the area of each coloured wedge, measured from the centre, is in proportion to the statistic it represents.")

The radius of the wedge is in proportion to the statistic it represents.