Item tree analysis (ITA) is a data analytical method which allows constructing ahierarchical structure on the items of a questionnaire or test from observed responsepatterns. Assume that we have a questionnaire with m items and that subjects cananswer positive (1) or negative (0) to each of these items, i.e. the items aredichotomous. If n subjects answer the items this results in a binary data matrix Dwith m columns and n rows.Typical examples of this data format are test items which can be solved (1) or failed(0) by subjects. Other typical examples are questionnaires where the items arestatements to which subjects can agree (1) or disagree (0).Depending on the content of the items it is possible that the response of a subject to anitem j determines her or his responses to other items. It