For external validity (representativeness of the sample), seven studies reported representative sample (probability sampling) of the targeted population and two studies reported a broad sample (the whole population was included in the study) [ 40, 44].
Elsewhere, we reported the representativeness of participating sites according to Australian population distributions [ 13].
In studies in which only positive findings were reported, the representativeness of these data are unclear.
These subsequent publications will also report on representativeness of the clients, midwives, and midwifery practices that participated in the DELIVER study.
In summary, due to a lack of clarity of reporting, assessing sample representativeness was not possible in many studies.
As with most systematic reviews there were methodological issues with many of the primary studies with variable quality in sampling, representativeness and reporting.
Although our sample suggested Ryff completers were more likely to be of higher socio-economic backgrounds than non-completers, comparative studies using the PWB in nationally representative samples e.g. MIDUS and NSFH [ 7, 14] do not report details regarding representativeness or non-completion.
Sample representativeness reported a 'high risk of bias' across most studies.
No study reported setting-level representativeness, and for three studies, this element was considered not applicable because the intervention was implemented in only one setting.
In previous publications, we have reported on the representativeness of the participating mothers and children and find, as with many cohorts, that less affluent and younger mothers were less likely to continue to participate, but the baseline maternal BMI does not differ between responders and non-responders.
