The perception of experts that migrants are a vulnerable group of workers is, however, quite difficult to further substantiate with quantitative data, at least in Britain and the Netherlands. In these countries the available data are either not differentiated or insuffi- ciently differentiated to be able to make such judgments. More- over, in all three European countries an exposure measure for occupational risks is lacking to convert these figures to comparable ratios. Whether more accidents happen to migrants cannot be established on the basis of these data.