Fig. 1From: Effects of pre-notification, invitation length, questionnaire length and reminder on participation rate: a quasi-randomised controlled trialParticipation rates for each dispatch arms. * P-values of participation to one or two components are shown. a + = presence of pre-notification; − = absence of pre-notification. b + = long invitation letter; − = short invitation letter, c + = long questionnaire; − = short questionnaire. d + = presence of reminder; − = absence of reminderBack to article page