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Under certain conditions, statistical evidence is more persuasive than anecdotal evidence in supporting a claim about the probability that a certain event will occur. In three experiments, it is shown that the type of argument is an important condition in this respect. If the evidence is part of an argument by generalization, statistical evidence is more persuasive compared with anecdotal evidence (Experiments 1 and 2). In the case of argument by analogy, statistical and anecdotal evidences are equally persuasive (Experiments 2 and 3). However, if the case in the anecdotal evidence is dissimilar from the case in the claim, statistical evidence is again more persuasive (Experiment 3). The implications of these results for the concept of argument quality are discussed. Zhaiyao Author Note Dans quelles conditions les preuves statistiques sont-elles supérieures aux preuves anecdotiques en soutien á une affirmation? Le rôle du type d'argument Hans Hoeken (Ph.D., University of Tilburg, 1995) is a professor at the Department of Business Communication Studies, Centre for Language Studies, Radboud University Nijmegen, the Netherlands. His research focuses on language and persuasion. Lettica Hustinx (Ph.D., Radboud University Nijmegen, 1996) is an associate professor at the department of Dutch language and culture, Centre for Language Studies, Radboud University Nijmegen, the Netherlands. Her research interest focuses on argumentation and persuasion. This research was supported by a grant from NWO (360-80-020), the Dutch Research Foundation. We thank Hans Beentjes, Berna Hendriks, Margot van Mulken, Donna Rouner, and two anonymous reviewers for their insightful comments and advice on earlier versions of this paper. Résumé Correspondence concerning this paper should be addressed to Hans Hoeken, Department of Business Communication Studies, Radboud University Nijmegen, P.O. Box 9103, NL 6500 HD, The Netherlands. E-mail: . [ABSTRACT FROM AUTHOR]

Clinical and research staff who work around magnetic resonance imaging (MRI) scanners are exposed to the static magnetic stray fields of these scanners. Although the past decade has seen strong developments in the assessment of occupational exposure to electromagnetic fields from MRI scanners, there is insufficient insight into the exposure variability that characterizes routine MRI work practice. However, this is an essential component of risk assessment and epidemiological studies. This paper describes the results of a measurement survey of shift-based personal exposure to static magnetic fields (SMF) (B) and motion-induced time-varying magnetic fields (dB/dt) among workers at 15 MRI facilities in the Netherlands. With the use of portable magnetic field dosimeters, >400 full-shift and partial shift exposure measurements were collected among various jobs involved in clinical and research MRI. Various full-shift exposure metrics for B and motion-induced dB/dt exposure were calculated from the measurements, including instantaneous peak exposure and time-weighted average (TWA) exposures. We found strong correlations between levels of static (B) and time-varying (dB/dt) exposure (r = 0.88–0.92) and between different metrics (i.e. peak exposure, TWA exposure) to express full-shift exposure (r = 0.69–0.78). On average, participants were exposed to MRI-related SMFs during only 3.7% of their work shift. Average and peak B and dB/dt exposure levels during the work inside the MRI scanner room were highest among technical staff, research staff, and radiographers. Average and peak B exposure levels were lowest among cleaners, while dB/dt levels were lowest among anaesthesiology staff. Although modest exposure variability between workplaces and occupations was observed, variation between individuals of the same occupation was substantial, especially among research staff. This relatively large variability between workers with the same job suggests that exposure classification based solely on job title may not be an optimal grouping strategy for epidemiological purposes. [ABSTRACT FROM AUTHOR]