Summary Part 1 describes the epidemiology of Hodgkin's disease occurring in those parts of the United Kingdom which are included in the Leukaemia Research Fund data collection survey. A total of 1,023 cases diagnosed between 1984 and 1986 were available for analysis. At county and district levels there was little heterogeneity in the distribution of cases. However, at the electoral ward level there were real differences for the younger age group . In this paper methods of investigation which are not dependent on census boundaries are applied and the presence of localised spatial clustering is confirmed. There is some evidence that the pattern of clustering relates to the nodular sclerosing subtype. These results are related to hypotheses of an infectious aetiology.The distribution of Hodgkin's disease has raised questions of long-standing interest to epidemiologists. The unusual agedistribution was first noted by MacMahon (1966), who suggested that it might result from a combination of two distinct diseases. From the histological appearance, clinical course and anatomical distribution of the lesions as well as the age distribution he postulated an infectious aetiology in those aged less than 35 and an aetiology similar to other lymphomas in cases over 50. Subsequent research is in broad agreement with the two disease hypothesis (Roush, 1987;Gutensohn, 1982). Evidence for a viral aetiology comes from anecdotal reports of micro-clusters and of case linkage (Vianna et al., 1971;Grufferman et al., 1977), from school cohort studies (Vianna & Polan, 1973), formal analyses of space-time interaction (Kryscio et al., 1973;Greenberg et al., 1983), case-control studies of social linkage (Zack et al., 1977;Scherr et al., 1984), and follow-up of cases of infectious mononucleosis (Rosendahl, 1974; Muellar, 1987). Although the evidence is inconclusive and somewhat conflicting there is a consensus that an infectious aetiology is more likely for younger cases.The Leukaemia Research Fund data collection survey has been described (McKinney et al., 1989) and the basic descriptive epidemiology of Hodgkin's disease reported. This showed some evidence of localised aggregations of cases, or 'clustering', for the younger age group. The present study concentrates on spatial clustering using more sophisticated methods of analysis which do not depend on arbitrary administrative boundaries.
MethodsIncidence data have been taken from the Leukaemia Research Fund data collection survey (DCS) described earlier (McKinney et al., 1989 al., 1989;Besag, 1989) and by control locations in the second (Cuzick & Edwards, 1989). Both provide global tests of the extent of localised spatial clustering. The NNA method involves consideration of each case in turn. We first identify the two nearest cases and then estimate the population from which these cases derived. If the expected number in this population is significantly small (P<0.05) then the case is the centre of a small local aggregation and is said to be 'clustered'. In a random distribution approxi...