Analysis of the 'epidemic' of multiple sclerosis in the Faroe Islands. II. Biostatistical aspects.
A series of biostatistical tests were applied to the data upon which the Faroe epidemic hypothesis was constructed. Temporal, cluster analysis using three commonly applied methods were unsuitable because of the very small size of the sample (32 cases of MS). Methods to detect non-random clusters of disease identified a cluster of 16 cases with date of onset between 1941-1950 (p less than 0.05). However, when 1 questionable case of MS was excluded, the resulting cluster did not support the epidemic hypothesis. The overlapping 95% confidence limits of 5- and 10-year based incidence rates of MS, by date of onset (Poisson distribution) argues against the presence of an epidemic. Analysis of the exposure data, i.e. contacts between the Faroese and the British troops, yielded only borderline statistical significance but changing a single case of MS from the exposed to the unexposed category failed to support the exposure theory. All calculations were also carried out using the probable date of acquisition of the disease, between the ages of 5 and 14 years; these also failed to substantiate the hypotheses of epidemic and transmissibility. Since the validity of statistical analysis to test for the presence of epidemics with small sample sizes is not well established, the lack of concordance between the results of the various approaches leads to the conclusion that there was no epidemic of MS in the Faroes.
Poser
C M
CM
Department of Neurology, Harvard Medical School, Boston, Mass.
Hibberd
P L
PL
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003718:Denmark; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000209:etiology / Q000635:transmission; D013029:Space-Time Clustering