Comparative research on the history of work is severely hampered by confusion regarding occupational terminology across time and space. This is regrettable as occupations form a key variable in many fields of history, ranging from research into stratification and mobility, through demography, to studies of labour markets and production. Within these fields, it is often desirable, and sometimes essential, to make comparisons between regions and periods.
The problems caused by the difficulties of interpretation have been evident in the field of stratification and mobility, where social position as indicated by occupation is a crucial issue. Indeed it is frequently noted by historians that observed differences between tables of occupational mobility may very well be due to incompatibility between coding schemes or due to classification errors. Even when dealing with contemporary survey material in the social sciences, where the problem is arguably less severe, the same doubts on the validity of international comparisons due to anomalous approaches to classification have often been voiced.
Goldthorpe, for example, has noted that in many contemporary studies on social mobility: "there is invariably a passage in which methodological problems and, in particular, problems of comparability of cross-national data are discussed and acknowledged to be grave. But then, this ritual having been completed, the analysis of the data goes ahead, even with a variety of caveats.
The possibility that seems not to be contemplated, however, is that the degree of unreliability in the data is such that analyses should simply not be undertaken; that rather than such analyses being of some value as 'preliminary' studies, which may subsequently be improved upon, they are in fact no more likely to have some approximate validity than they are to give results that point entirely in the wrong direction."
It seems clear then that comparisons of important historical structures and processes would be a little less problematic if comparability in the coding of occupations was achieved. Such is the aim of HISCO..