PONE-D-20-18902

External validity of prevalence estimates from the National Maternity Surveys in England: the impact of response rate

PLOS ONE

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Reviewer #2: Yes

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Reviewer #1: This is an extremely important paper. As survey response rates have been dropping, the field of survey research and users of survey data are very interested in whether lower response rates indicate lower accuracy of survey measurements. This paper uses unique and impressive data to do the type of analysis that is extremely difficult for most surveys: to benchmark against official records that are likely to be highly accurate. The findings, that lower respondents rates do not indicate lower accuracy, align with a few other papers exploring the same sorts of issues with very different types of data. Therefore, this paper is extremely valuable at this time and will be very highly cited if it's made sufficiently visible. Also, the paper is really helpful by exploring whether conventional weighting increases accuracy of survey estimates - the evidence of improved accuracy due to weighting is important, because this methodology has usually been taken for granted and has rarely been subjected to empirical testing. So this testing is very helpful. Also helpful is the evidence that the accuracy of these surveys was generally extremely high - that, too, will cause the paper to be heavily cited, for good reason. And the evidence here that "true" rates often fell outside the margin of error of the survey estimate is a useful wake-up call telling researchers that these margins of error are most likely misleadingly small.

I commend the authors for working on an extremely important topic, using impressive data, doing thorough and thoughtful analyses, and generating extremely valuable results.

I have two suggestions: First, the authors should cite more thoroughly the small number of previous publications exploring the impact of response rates on survey accuracy, including Curtin et al. (POQ), Keeter et al. (POQ), Merkle and Edelman (book chapter), Holbrook et al. (book chapter).

Second, and more serious, I appreciate the authors' discussion of breastfeeding, but there's a problem here. Treating unknown breastfeeding status as not breastfeeding no doubt (as the authors say) biases those numbers downward from the routine data. And unlike the other measures, I presume that even the routine data for breastfeeding are based on parent reports rather than more objective data. So I would strongly suggest a different approach to breastfeeding: (1) be much more explicit with readers about how the routine data measurements were made, (2) tell readers the proportions of babies for whom breastfeeding was not known in each survey, (3) if those numbers are large enough, consider dropping the breastfeeding data from the paper altogether, (4) if those data are not dropped, discuss them completely separately from all other data, making it much clearer to readers that the routine data on breastfeeding may be problematic enough to undermine the value of the analyses with that variable.

Reviewer #2: This paper investigates the accuracy of population estimates derived from the National Maternity Survey across varying levels of response rates obtained between 2006 and 2018. Survey estimates are compared with gold standard with information obtained NHS Digital. For the two most recent surveys, weighted and unweighted survey data can both be compared. The analyses conclude that there is no association between accuracy of estimates and survey response rates. The paper is well-done. The writing is clear, the data are of high quality, the statistical analyses are excellent, and the findings make good sense. A valuable finding and conclusion is that the accuracy of survey estimates seem to vary by question topic. I frankly see little to quibble with in this manuscript and believe it will be a useful contribution, specifically to the field of health survey research methodology.

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External validity of prevalence estimates from the National Maternity Surveys in England: the impact of response rate

PONE-D-20-18902R1

Dear Dr. Harrison,

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Kind regards,

Diane Farrar

Academic Editor

PLOS ONE