Background: The DSM-IV definition of hypochondriasis is contrasted with hypochondriacal dimensions as provided by the Whiteley Index (WI) and Illness Attitude Scales (IAS).
Methods: Exploratory factor analysis was conducted on self-report data from 570 patients with mental and psychophysiological disorders. Of these, 319 were additionally diagnosed according to DSM-IV by structured interviews.
Results: The three 'classic' factors of the WI labelled disease phobia, somatic symptoms and disease conviction were confirmed. The IAS consisted of two dimensions indicating health anxiety and illness behaviour. The overall scores of both instruments were highly correlated (0.80). Optimal cut-off points for case identification yielded sensitivity/specificity rates of 71/80% (WI) and 72/79% (IAS). The IAS was superior to the WI when patients with hypochondriacal disorder were to be discriminated from non-hypochondriacal somatizers. Largest group differences were found for scales related to affective components (health anxieties), smallest for illness behaviours. Affective components of hypochondriasis explained more variance of diagnostic group membership than somatization symptoms. The subscales of disease phobia (WI) and health anxiety (IAS) were most sensitive to treatment-related changes.
Conclusions: The self-rating scales are valid for screening, case definition and dimensional assessment of hypochondriacal disorder, including the differentiation between hypochondriasis and somatization. The existence of distinguishable affective and cognitive components was confirmed.