Changes in butterfly distributions: a simple correction for bias caused by sub-sampling of atlas records makes no difference to BAP status

In order to compare two sets of butterfly atlas data for the U.K. contrasting in number of records, a process of sub-sampling has been applied by Butterfly Conservation UK. This procedure has been criticised on two counts by Barbour, first on the basis of being taken to an excessive level; secondly, for creating bias in trends (losses, gains) among species. The present paper provides a simple correction for the second issue resulting from potential bias created by sub-sampling of records to determine incidence within 10 km squares. It demonstrates that any bias has not influenced the Biodiversity Action Plan status of butterflies in the U.K.