16 August 2011

A histogram for Albinaria

Regular readers may have noticed that one of my passions is to measure snail shells. I have written about the variability of shell dimensions on several occasions, for example here. Naturally, I have pages and pages of data waiting to be analyzed and made sense out of.

Today, I entered a set of measurements from 2004 into the computer. They belong to a sample of 131 shells of an Albinaria species that we had collected in 2002 in Turkey. Here is the histogram for shell heights.

I haven't run any statistical tests, but the distribution looks roughly normal. The 2 specimens making up the right-hand tail seem to be outliers. However, the relative coefficient of variation* is 5.8%, which is quite ordinary for shell heights of tall-shelled land snails. So those 2 shells actually lie within the expected range of variation for a sample of this size.

The 2nd entry in this series is here.

*(standard deviation/mean)x100


Snailbum said...

Are these all "adult" Albinaria, that is, ones with the definitive aperture that marks the end of spiral growth for a given snail?


Yes, they are all adults with more or less intact bottom lips. Thanks for pointing that out. I should have mentioned that in the post.