Vagaries in the delimitation of character states in quantitative variation--an experimental study

An experimental study on the delimitation of character states in continuous variation indicates that (1) the way data are presented influences the assignment of character states and (2) states in the same data set are delimited in various ways by different individuals. Forty-nine individuals were given a set of graphs denoting variation of 10 characters in the genus Kalmia (Ericaceae) and outgroups, all identification having been removed from the graphs. The variation was represented in one of three ways: as 95% confidence intervals on a linear scale, as 95% confidence intervals on a log10 scale, or with bars showing SD x 2 on a linear scale. No two individuals scored a set of graphs in the same way, and only one character in one representation was scored identically by all individuals; the scoring for this character was completely different when the ordinate was changed from linear to logarithmic. Together, the 49 individuals delimited states within each character between 9 and 16 different ways. In general, variation represented by 2 x SD bars elicited the largest numbers of different scorings, yet with a relatively low number of states; the complexity of the patterns in the graphs in this representation was greatest. Expert knowledge appears to be of dubious value in delimiting states in such variation, and if such characters are to be used in phylogenetic analyses, states could be delimited by people who know nothing of the details of the study being scored; in any case, presentation of data and an explicit protocol to follow when delimiting states are essential. In converting data of this type into character states, psychological factors are particularly likely to come into play. Other implications of our experiments include the severe underdetermination of some phylogenetic hypotheses by observation and the heterogeneous nature of morphological data.