Neurobehavioral deficits and parkinsonism in occupations with manganese exposure: a review of methodological issues in the epidemiological literature.

Although the parameter estimate for a linear effect on Digit Span was highly significant ( p = 0.001), most of the outcomes did not exhibit statistically significant linear trends, perhaps because much of the performance decline had already occurred within the lowest cumulative exposure category, resulting in a nonlinear relationship over the observed range of cumulative exposure.

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A composite score of clinical abnormalities was significantly elevated comparing the medium- and high-exposure workers with the low exposure group (one or more abnormalities: OR = 3.7, 95% CI = 1.1,13), and a significant trend of the clinical abnormalities score across quartiles of MnB was also observed.

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