Change index: a measure of change in range size that is independent of changes in survey effort

Change index: a measure of change in range size that is independent of changes in survey effort A major problem in studying the range changes of invertebrates using atlas data, is discriminating the effects of changing survey effort from the real biological changes. Using the data sets collated by the UK Biological Records Centre, a method has been developed which allows for the effects of variation in survey effort, by calculating an index of relative change in range size. The method is applicable to a wide range of atlas data sets