Moss, D. and Pollard, E. 1993. Calculation of collated indices of abundance of butterflies based on monitored sites. Ecological Entomology
Pollard, E and Yates, T.J. 1993. Monitoring butterflies for ecology and
conservation. London: Chapman and Hall.
Pollard, E. 1977. A method for assessing changes in the abundance of
butterflies. Biological Conservation 12, 115-134.