Abstract
The potential for bias, i.e., influences that cause results to deviate systematically from the truth is substantial both in toxicological research and in the performance of standardized toxicological testing. In this contribution, major potential sources of bias in toxicological research and testing are identified. Due to the lack of empirical studies of bias in toxicology, very little is known about its prevalence and impact. Areas to consider for such studies are pointed out, and it is suggested that such investigations should be given priority.
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Notes
It should be noted that in cases where research or toxicity testing is performed with the aim to enable a human health risk assessment there would be a potential for a biased choice of experimental model: more often than not important information about species differences in sensitivity towards a specific exposure is missing, and therefore we have a restricted understanding of the extent to which the animal model is representative of humans. Sometimes the animal model will overestimate human toxicity (creating a false positive result), and sometimes it will be less sensitive than humans (creating a false negative result). In both of these cases a bias has been introduced in the process, given the ultimate aim of a reliable human health risk assessment. This issue, however, is more pertinent to a discussion of possible biases in risk assessment (rather than in toxicology), so we will not pursue it further in the present contribution.
Standardized testing may still of course be supplemented with determination of certain mechanistic data in order to adjust the testing procedure or to facilitate the interpretation of data.
For examples from the EU, see for instance: Council Directive 67/548 and 92/32/EEC defining the base-set of data required for risk assessment; Council Regulation 793/93/EEC defining how data reporting should be conducted; Directive 2001/83/EC and Commission Directive 2003/63/EC regulating the safety assessment of pharmaceuticals for human use; Council Directive 91/414/EEC concerning plant protection products; Council Directive 76/768/EEC concerning cosmetic products; Council Directive 89/107/EEC concerning food additives; Directive 98/8/EC concerning biocides. In other jurisdictions corresponding regulation can be found.
The total number of government-funded studies was 119, and the total number of industry-funded studies was 11.
See for instance the OECD test guidelines for carcinogenicity testing (no. 451), for chronic toxicity testing (no. 452) or for the two-generation reproductive toxicity test (no. 416).
Obviously, whether a result is interpreted as significant or not also depends on which confidence interval is used. However, that choice is almost always governed by conventions, and does not in practice differ between studies.
The absolute probability of a false positive is equal to p(R& H0) = p(H0)·p(R|H0) where H0 is the null hypothesis and R the outcome of the experiment.
Studies carried out under GLP are subject to inspection by an internal quality assurance programme, which is, among other things, responsible for performing an audit of raw data and the final report, ensuring that the data are complete and that they have be accurately reported (OECD Series on Principles of GLP and Compliance Monitoring, no. 4).
This is possible when investigating publication bias within medical research involving human subjects because such research must be approved by an authority (usually an ethics committee) before being carried out. For examples of such investigations, see Easterbrook et al. (1991) and Stern and Simes (1997).
In the US, data from studies that are funded by federal agencies must be made available to the public. For a critical discussion of this, see Crissman et al. (1999).
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Acknowledgements
This work was funded by the Swedish Research Council for Environment, Agricultural Sciences and Spatial planning (FORMAS), and the Swedish Foundation for Strategic Environmental Research (MISTRA). An earlier version of this paper was presented at a seminar hosted by professor Helen Håkansson at the Institute for Environmental Medicine, Karolinska Institutet. The authors wish to thank participants in that seminar for helpful comments.
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Wandall, B., Hansson, S.O. & Rudén, C. Bias in toxicology. Arch Toxicol 81, 605–617 (2007). https://doi.org/10.1007/s00204-007-0194-5
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DOI: https://doi.org/10.1007/s00204-007-0194-5