Norber Erratics

The “Norber Erratics” are a collection of rocks well known to geography students. At the end of the last ice-age they were sitting on the ground surface, and ever since the ground has been slowly weathering away, leaving them standing on stubby plinths. What we have here is a set of measurements, 4 for each boulder, showing the height above the modern ground-level in cm of the top of each side. Rather than plot 4 separate charts, GraPL has been asked to construct a Trellis Plot and the frequency histograms for the 4 compass directions are laid out in a neat grid.

View example as VML

View example as SVG

It looks as though the South-facing side is the odd one out here, and another very good way to compare the data would be to make a Box and Whisker plot of the heights:

View example as VML

View example as SVG

This shows the median value, the quartiles and the extreme range of each set of data. Now it really looks quite convincing that the south-facing side is higher.