Distributions of the BioNJ bootstrap-based confidence values on the true branches of model trees estimated from initial (non-trimmed) multiple sequence alignments and from alignments returned by seven character trimming methods. Average confidence values are written under each corresponding histogram. For each level of divergence, the best (i.e. higher) average confidence value is written in boldface characters. Average confidence values associated to distributions that are not significantly different to this best distribution (as assessed by a χ2 test) are underscored.