Information on study size in epidemiological studies
Total: all registered persons from a particular database (e.g. residents' registration office, cancer register).
Eligible: persons from the total number who meet certain conditions (diagnosis) and are not excepted because of exclusion criteria.
Contacted: eligible persons who are invited to participate in the study verbally or in writing.
Participants: number of eligible and contacted persons who actually participate in the study. This excludes, for example, persons who do not want to participate, could not be reached, or do not have sufficient language skills.
Participation rate: percentage of contacted persons who participate in the study.
Evaluable: number of participants who were regularly examined during a certain period (follow-up) or whose data was completely collected.
There is a top-down decrease due to the fact that each stated number is a subset of the preceding number. A study does not necessarily contain all values.