Since in wave 4 only native Dutch survivors participated, these models were run on this subgroup of the study population.
Overall, 112 units (57% of those invited) actively participated; these units were representative of all those in the CMP.
For this research we asked written permission from all participated these health care institutions to use their CQ Index data for scientific purposes, and all institutions cooperate.
Of 2,257 eligible population controls, 1,381 (61.2%) participated (these were considered the original control population), 658 (29.1%) refused to participate, and 218 (9.7%) did not respond.
In addition, four midwives involved in conducting the first antenatal booking visit expressed interest and participated (these midwives represented four maternity services that had not been contacted to participate).
A potential limitation of our practice surveillance study is that although the majority of all paediatric practices in the area participated, these practices may not be fully representative of the population investigated.
