The first question is HWE is common. Any occupational study looking for the worker health could potentially faced this problem. When we made computer search in medline from the year 74; when it was first named-we found 59 articles with HWE in its title. an extra search in other occupational database result in additional 20 articles with HWE in the title. More than 400 articles contain HWE in the content. So its a common problem.