We have tried to find all cases of motor neuron disease (MND) with onset during the study period 1961-1990 in the county of Skaraborg, Sweden, and in this retrospective study we have identified 168 cases, 107 men and 61 women. Fifty percent of them were alive 2 years after onset. The number of MND cases in consecutive 5-year intervals during the study period was shown to be statistically significantly elevated for males in the period 1981-1985 (Knox test disjoint procedure, p = 0.02). During the period 1973-1984, 70 males had onset of MND, corresponding to an average annual incidence of 4 per 100,000 person-years. This epidemic-like cluster was compared to the MND morbidity in a neighbouring county and was shown to be statistically significantly elevated even when the p value was adjusted for multiple comparisons. Agricultural work was significantly more common among the cases compared to the rest of the population.
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Gunnarsson et al. (1996) studied this question.