1. T. Sorensen. A Method of Establishing Groups of Equal Amplitude in Plant Sociology Based on Similarity of Species Content and Its Application to the Analyses of the Vegetation on Danish Commons. Biologiske Skrifter, vol. 5, no. 4, pp. 1–34, 1948.
2. P. Sneath. The Application of Computers to Taxonomy. Journal of General Microbiology, vol. 17, no. 1, pp. 201–226, 1957.
3. R. R. Sokal, P. H. A. Sneath. Principles of Numerical Taxonomy, W. H. Freeman, San Francisco, USA, 1963.
4. J. H. Ward. Hierarchical Grouping to Optimize an Objective Function. Journal of the American Statistical Association, vol. 58, no. 301, pp. 236–244, 1963.
5. M. R. Anderberg. Cluster Analysis for Applications, Academic Press, New York, USA, 1973.