Methodological Problems in the Neuropsychological Assessment of Effects of Exposure to Welding Fumes and Manganese

Abstract

Recently, Kaiser (2003) raised concerns over the increase in brain damage claims reportedly due to exposure to welding fumes. In the present article, we discuss methodological problems in conducting neuropsychological research on the effects of welding exposure, using a recent paper by Bowler et al. (2003) as an example to illustrate problems common in the neurotoxicity literature. Our analysis highlights difficulties in conducting such quasi-experimental investigations, including subject selection bias, litigation effects on symptom report and neuropsychological test performance, response bias, and scientifically inadequate casual reasoning.

Neurobehavioral Deficits and Parkinsonism in Occupations with Manganese Exposure: A Review of Methodological Issues in the Epidemiological Literature

“…Statistically significant negative associations were reported between duration in welding and verbal learning, auditory span, working memory, cognitive flexibility, and motor efficiency. Lees-Haley (who was hired by the defense in welding rod litigation) et al [44] dispute the findings of Bowler (who has worked for welding plaintiffs) et al [47], claiming that the ambiguous case derivation limits etiologic inference. Thus, the Bowler case series could merely represent a selection of prevalent movement disorder or other neurobehavioral outliers from a large welder source population that has a typical, expected distribution of these outcomes.…”

Searching for a relationship between manganese and welding and Parkinson’s disease

“…This study, however, has been criticized because of many methodologic problems, including the fact that welders had a lower educational background than controls. 91 Also, no attempt was made to correlate the abnormal neuropsychological findings with dose or duration of exposure. Furthermore, there was an obvious selection bias as the welders were recruited into the study because they filed civil and Workman's Compensation litigation claiming that their symptoms were related to occupational welding.…”

Potential neuropsychological profiles in welders occupationally exposed to manganese: An examination of effect size patterns

“…Spurious or chance findings are likely to emerge in studies that are conceptually, methodologically, and/or statistically flawed-such studies are considered to have poor internal validity. A recent article by Lees-Haley, Greiffenstein, Larrabee, and Manning (2004) documented the many flaws in the first Bowler et al (2003) study that was examined in the current research, as well as broader difficulties in studying the neurotoxic effects of manganese. For instance, these authors noted the following flaws in Bowler et al's existing research: selection bias, severe covariate imbalance, lack of neurobiological criterion, poor control of biased responding, and inadequate test selection.…”

“…For instance, these authors noted the following flaws in Bowler et al's existing research: selection bias, severe covariate imbalance, lack of neurobiological criterion, poor control of biased responding, and inadequate test selection. As just one example pointing to findings that are implausible, Lees-Haley et al (2004) noted that the White welders in the Bowler et al (2003) study performed significantly better on measures of fine motor skills (i.e., Grooved Pegboard & Finger Tapping Test) than they did on measures of gross motor skills (i.e., Dynamometer). They considered such a pattern atypical and unlikely, as the hierarchically organized motor system should first result in gross motor impairment, followed by fine motor impairment.…”