As predicted, positive excess item scores were associated with each item, confirming that the relationship between items was not random (Table 1). The mean excess score was 3.5 (s.d. = 1.0). However, the excess score varied between the items, ranging from 2.0 to 5.5. If the relationship between items is non-reflexive (i.e. their endorsement follows a hierarchical arrangement), the rarer items should be associated with a greater excess score than the more frequent ones. This is what we found. Thus, the excess symptom score associated with each item was significantly and strongly associated with the frequency of endorsement of that item (r = –0.79, P