• Epidemiology
• hygiene/occupational hygiene
• exposure assessment
• retrospective exposure assessment

First introduced 25 years ago, expert assessment of occupational exposure was an important innovation for community-based case–referent studies in occupational epidemiology.1 Here is a simplified scheme of how expert assessment is now practiced: detailed interviews of subjects are reviewed by ‘exposure assessment experts’ who then pass on to epidemiologists their best guesses of exposure status, which are then frequently used as if they are error-free in epidemiological analyses. This method is applied when there are no relevant measurements of exposure that are deemed suitable for mathematical/statistical exposure modelling. The article by Bhatti et al 2 presents this paradigm as state-of-the-art and attempts to support this a priori supposition in the context of a gene–environment interaction study. Therefore, it is legitimate to enquire how comfortable occupational health researchers should feel about such a conjecture and to gauge whether any alterations to the original concept are desirable.

Contrary to the claim by Bhatti et al,2 Teschke et al 3 never concluded that that expert assessment was “the best method”, but were careful to point out—too tactfully—that none of the exposure assessments methods commonly practiced in community-based case–referent studies of occupational aetiology were particularly good. The sentiment that expert assessment was not a panacea was forcefully reiterated in a commentary by Professor Kromhout3 on the outstanding review by Teschke et al. 3 Clearly, leading exposure assessors have grave doubts about value of expert assessment methodology as it is currently practiced.

Next we must examine what new evidence Bhatti et al …