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The effect of using only intercorrelated characters in a numerical taxonomic study was investigated using 74 external morphological characters of pupae in 45 species of North American mosquitoes. Correlation and distance coefficients were computed based upon standardized data. Cluster analyses and factor analyses were performed and compared. In addition, analyses were made of the correlation among the characters using centroid components analysis and multiple factor analysis with rotation to simple structure. The only effect of using correlated characters appears to be that it causes the generic clusters to appear very elongated in the n dimensional character space. Standard methods of cluster analysis have a tendency to make the OTU's at the ends of these clusters appear much more isolated than they “should be.” Methods for correcting for this bias were discussed.
F. James Rohlf (Thu,) studied this question.