Completion rate is a measure used to describe data collection procedure and quality of data collected in online survey (most often). It is number of fully completed interviews divided by the number of started interviews. Completion rate is not the same as response rate. For example. if 1000 persons were asked to take part in a survey, 100 of them accepted and 90 actually completed questionnaire then response rate is 10% (RR=100/1000) and completion rate is 90% (CR=90/100). Completion rate can provide information about survey instrument - if certain questions are not filled in more often then some other (i.e. have lower completion rate) then they are probably sensitive and if the interviewing is stopped or interrupted after some time then it is likely that survey procedure is exhausting (long questionnaire, for example).