The discussion of health inequalities in Britain (e.g. in the Black Report) has been conducted largely on the basis of social class mortality differentials measured by achieved social class and not by social class of origin. It is shown in this paper that social class mortality differentials by achieved social class are not invariant to the rate of social mobility and that the use of them is likely to result in a biased measure of trends in health inequalities when the absolute rate of social mobility varies over time. It is further shown that if, as is likely, health status is a factor systematically affecting the probability for an individual of upward or downward social mobility, then an increase in the rate of social mobility may well result in constant or widening social class mortality differentials by achieved social class even if the differentials are narrowing when measured by social class of origin. It is claimed that this process may well explain why the observed social class mortality differentials, which are measured by achieved social class, have not fallen in Britain during the post-1945 period.
* I would like to thank Raymond Illsley, Heather Joshi, David Metcalf and David Piachaud for their assistance and encouragement while writing this paper. The comments of a referee of the JSP were also very helpful for clarifying the argument of the paper. I would also like to acknowledge financial support from the Social Science Research Council. The arguments and the views expressed in this paper however, are, the responsibility of the author alone. They are not necessarily supported by any of the above or by any institution to which the author has been or is currently attached.
† Visiting Research Associate at the Centre for Labour Economics, London School of Economics and Political Science.