NIHR Policy Research Unit in Maternal and Neonatal Health and Care, National Perinatal Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Old Road Campus, Headington, Oxford, United Kingdom.
PLoS One. 2020 Nov 30;15(11):e0242815. doi: 10.1371/journal.pone.0242815. eCollection 2020.
Prevalence estimates from surveys with low response rates are prone to non-response bias if respondents and non-respondents differ on the outcome of interest. This study assessed the external validity of prevalence estimates of selected maternity indicators from four national maternity surveys in England which had similar survey methodology but different response rates.
A secondary analysis was conducted using data from the national maternity surveys in 2006 (response rate = 63%), 2010 (response rate = 54%), 2014 (response rate = 47%) and 2018 (response rate = 29%). Unweighted and (for the 2014 and 2018 surveys) weighted survey prevalence estimates (with 95%CIs) of caesarean section, preterm birth, low birthweight and breastfeeding initiation were validated against population-based estimates from routine data.
The external validity of the survey estimates varied across surveys and by indicator. For caesarean section, the 95%CIs for the unweighted survey estimates included the population-based estimates for all surveys. For preterm birth and low birthweight, the 95%CIs for the unweighted survey estimates did not include the population-based estimates for the 2006 and 2010 surveys (or the 2014 survey for preterm birth). For breastfeeding initiation, the 95%CIs for the unweighted survey estimates did not include the population-based estimates for any survey. For all indicators, the effect of weighting (on the 2014 and 2018 survey estimates) was mostly a shift towards the population-based estimates, yet the 95%CIs for the weighted survey estimates of breastfeeding initiation did not include the population-based estimates.
There were no clear differences in the external validity of prevalence estimates according to survey response rate suggesting that prevalence estimates may still be valid even when survey response rates are low. The survey estimates tended to become closer to the population-based estimates when weights were applied, yet the effect was insufficient for breastfeeding initiation estimates.
如果应答者和未应答者在感兴趣的结局上存在差异，那么来自应答率较低的调查的流行率估计值容易受到无应答偏倚的影响。本研究评估了英格兰四项全国性产妇调查中特定产妇指标的流行率估计值的外部有效性，这些调查具有相似的调查方法，但应答率不同。
使用 2006 年（应答率=63%）、2010 年（应答率=54%）、2014 年（应答率=47%）和 2018 年（应答率=29%）全国性产妇调查的数据进行二次分析。未加权和（针对 2014 年和 2018 年调查）加权调查流行率估计值（95%CI）的剖宫产、早产、低出生体重和母乳喂养开始情况与基于人群的常规数据估计值进行了验证。
调查估计值的外部有效性因调查和指标而异。对于剖宫产，所有调查的未加权调查估计值的 95%CI 均包含基于人群的估计值。对于早产和低出生体重，未加权调查估计值的 95%CI 不包括 2006 年和 2010 年调查（或 2014 年早产调查）的基于人群的估计值。对于母乳喂养开始，任何调查的未加权调查估计值的 95%CI 均不包括基于人群的估计值。对于所有指标，加权（对 2014 年和 2018 年调查估计值）的影响主要是向基于人群的估计值转移，但加权调查的母乳喂养开始估计值的 95%CI 不包括基于人群的估计值。
根据调查应答率，流行率估计值的外部有效性没有明显差异，这表明即使调查应答率较低，流行率估计值可能仍然有效。当应用权重时，调查估计值往往更接近基于人群的估计值，但对于母乳喂养开始的估计值，效果还不够。
