Survey of motivation to participate in a birth cohort.

For a longitudinal prospective cohort study to be successful, participants' motivation to provide information must be maintained. Therefore, this study aimed to identify items that effectively promote participants' motivation. Questionnaires were mailed to 4541 mothers and expectant mothers in Chiba Prefecture, Japan who participated in a nationwide birth cohort. A total of 2387 (52.6%) responses were received. The following items were identified as primary motivating factors among our cohort: "benefits to the participants' children", "monetary compensation" and "contribution to a better future environment". More than 30% of the respondents expressed a lack of understanding regarding the study purpose and requirements for participation. About 14% were concerned about the leakage of personal information, and 13% felt burdened by having to make a long-term commitment to the study. Cluster analysis identified four groups, two of which, one with extremely low levels of motivation and the other motivated by only money or goods, lacked an understanding of the study and tended to be concerned about the associated risks and burdens. Participants in these groups were considered to be at a high risk of dropout. Therefore, implementing measures to provide participants with a better understanding of cohort studies could lead to more successful results.