Marcel Slockers

30 Chapter 2 Methods Ethics statement The Medical Ethical Review Committee of the Erasmus MC declared that this study was not subject to the Law on Medical Research with human beings and that it had no objections to the performance of this study. Study population Cohort of homeless people Institutions providing care to homeless people in Rotterdam were approached to provide full name, date of birth and sex of persons who visited their facility in 2001. This information was largely available because in 2001 homeless people were counted during research on the homeless in Rotterdam. 23 Institutions subsidized by the local government and services provided by the church were included, covering services at different locations in Rotterdam. These care facilities provide many services to homeless people (including those sleeping rough), ranging from the provision of meals, to night-care facilities and convalescence care for ill homeless. Pooling the lists from the different facilities yielded 5810 records: removal of duplicates with same name, initials/surname, date of birth and sex yielded 3398 persons. The study on Rotterdam homeless conducted in 2001 counted 4607 homeless people. 23 The difference between this higher number compared with our cohort of 3398 persons may be because non-Dutch EU citizens and illegals not in the Dutch municipal population registers may have used care services in 2001, and the 2001 total of 4607 persons may have included duplicates. In the present study, the deletion of duplicates may have been more efficient due to the availability of several computerized registries. We used a restrictive matching procedure to ensure that for all matched persons we could determine in the municipal population registers whether (and if so when) that person had died. Of the 3398 persons in our cohort, 2159 provided a match with the municipal population registers (which include information on vital status and date of mortality). A total of 7 persons had died before the start of the follow-up. In addition, we excluded persons aged under 20 years to allow comparison with administrative data in 5-year age groups (e.g. 20–24 years) and to avoid the low mortality rates below age 20 years. Finally, our study population consisted of 2096 persons.