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Weaknesses of birth certificate follow-back
surveys include that they are resource intensive, particularly given the
high level of effort to track children which is particularly difficult with
highly mobile populations. These studies do not include children who
immigrate into the study area and often exclude children who migrate out of
the study area due to resource limitations and it may not be possible to
find these children. Additionally, completion rates are often low (80% or
less) which has the potential to introduce bias if coverage differs among
children for whom data are collected compared with children who can not be
found or data are not collected. As with any measure of immunization
coverage, the validity of data may not be good if the immunization histories
are not verified or validated. |