Problems with characterization occupational exposures

The case-control method does have its problems. Characterization of past exposure experiences by both cases and controls is sometimes based on memory. Individuals will be able to recall their occupations, but may not be able to pinpoint specific chemicals. They almost certainly can not specify the quantity of exposure (chemical concentrations), although they may perhaps recall the total time they were exposed. Study interpretation is sometimes complicated by the possibility that cases and controls may differ in their recollections of past exposures if this is the case (and it s not easy to tell if it is), the study may not meet the criteria expected for a truly controlled situation. In some cases recollection can be checked by turning to documentary records of those exposures, but past record keeping on most occupational exposures was typically irregular and incomplete. Other problems exist in selecting appropriate controls, and there are sometimes serious technical difficulties associated with statistical analysis of study results. 

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