Case-control study on uveal melanoma (RIFA): rational and design

BMC Ophthalmology

Table 2 Inclusion and exclusion criteria of three different control groups of the RIFA case-control study

Characteristics
	Population control	Ophthalmologist control	Sibling control
Age	Within 5 year age group of case¹	Within 5 year age group of case¹	Age within +/- ten years compared to age of case. If more then one sibling lies in this range, the one closest to the case is chosen, unless he/she refuses. If so, the sibling fitting second best in age is chosen.
Sex	The same sex as case	The same sex as case	The same sex as the case; when a same sex sibling does not exist or refused, then the opposite – sex sibling is chosen.
Reference period		Visit at the ophthalmologist's within 10 working days (possibly more)² before reference date set by case diagnosis.
Diagnosis	No history of cancer	No history of cancer	No history of cancer
Language	Being capable to complete the interview in German	Being capable to complete the interview in German	Being capable to complete the interview in German
Region of residence	Residence matched to case³	Germany

1) The reference date is the date of the case diagnosis 2) With small ophthalmologist's practices it may become necessary to increase the span of ten working days in order to recruit ten eligible patients. 3) As residence matching is not performed at the level of single cities, controls will be taken from a sample in a city comparable size within a radius of 60 km around the case's habitation, if such a sample exists.

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