New modelled estimates of maternal mortality – Authors' reply
Authors: Chris Murray
Journal: The Lancet (2010)

We appreciate the rich set of letters in response to our paper on maternal mortality. The authors of the letters raise many important points, but we focus our short response on four larger themes that have been raised. The country graphs in the webappendix to our paper show all the available data points for each country and our best estimates based on these data and the modelling strategy. In the case of the Philippines, Indonesia, Burkina Faso, and Peru, the correspondents have noted that our data-points derived from the analysis of sibling histories in household surveys are different from published figures from the same surveys. The differences stem from two sources. First, we correct for problems of survivor bias in sibling histories, following the published methods of Gakidou and King1Gakidou E King G Death by survey: estimating adult mortality without selection bias from sibling survival data.Demography. 2006; 43: 569-585Crossref PubMed Scopus (72) Google Scholar and Obermeyer and colleagues.2Obermeyer Z Measuring adult mortality using sibling survival: a new analytical method and new results for 44 countries, 1974–2006.PLoS Med. 2010; 7: e1000260Crossref PubMed Scopus (70) Google Scholar Second, we use the proportion of reproductive-aged female deaths related to pregnancy and then multiply this by the levels of adult female mortality estimated through the systematic assessment of all sources published by Rajaratnam and colleagues.3Rajaratnam JK Marcus JR Levin-Rector A et al.Worldwide mortality in men and women aged 15–59 years from 1970 to 2010: a systematic analysis.Lancet. 2010; 375: 1704-1720Summary Full Text Full Text PDF PubMed Scopus (129) Google Scholar This systematic analysis uses the sibling history data, and corrects for both survivor and recall biases as well as using other sources of mortality data such as vital registration or census data. Estimates direct from sibling histories that do not take these factors into account can be substantially biased downwards in some countries. Fernando Althabe and colleagues note that our estimates for Argentina based on vital registration are higher than officially reported figures. This difference is due to correcting for misclassification of maternal deaths following the methods published by Naghavi and colleagues.4Naghavi M, Makela S, Foreman K, O'Brien J, Lozano R. Algorithms for enhancing public health utility of national causes of death data. Popul Health Metr (in press).Google Scholar This correction ranges from 21·3% to 45·9%. Further, we include 3·0% of maternal deaths due to late maternal deaths. By contrast, Affette McCaw-Binns and Karen Lewis-Bell argue that our correction for misclassification in Jamaica provides estimates that are lower than unpublished data from a national surveillance system. The latest vital registration data available to us or to WHO for Jamaica is from 1991, which yielded with correction for misclassification a maternal mortality ratio (MMR) of 50 maternal deaths per 100 000 livebirths. The trend from 82 in 1980 to 34 in 2008 is based on the model predicted on the basis of trends in the neonatal mortality rate, maternal education, income, and HIV seroprevalence. Our webappendix provides a substantial discussion of the types of uncertainty that can and should be included in the estimates of the MMR and the choices we have made in this paper. On one point, Wendy Graham and colleagues are correct that we have not included uncertainty in the levels of adult female mortality, as published by Rajaratnam and colleagues, in the final uncertainty intervals. However, we have included in our assessment a large component of uncertainty from non-sampling variance, which would ideally not be included in the uncertainty intervals for the expected value of the MMR. This overestimate is quite large, so we believe that, for most countries, our published uncertainty intervals are still too wide, rather than too narrow. Of note, because non-sampling variance is correlated over time, naive interpretation of uncertainty intervals in one year compared with another will dramatically exaggerate uncertainty in trends. More generally, current practice in reporting uncertainty intervals for descriptive analyses such as mortality rates and causes of death in global studies needs to be more standardised. We have been much more systematic in estimating uncertainty than previous studies to date, but we believe that the global health community would benefit from more standards on what sources of uncertainty should be propagated into final estimates. Graham and colleagues are also concerned that through the process of peer review some of our results changed. We believe that authors should be responsive to important issues raised through the process of peer review. In our view, our results have been improved through our extensive and rigorous response to issues raised by multiple reviewers. As more experts in each country carefully evaluate our findings, we are sure that other data sources will come to light that have not been included in our analysis. Given that our methods are transparent and replicable, it will be possible for other researchers or ourselves to re-estimate maternal mortality taking into account new evidence that becomes available in the public domain. New modelled estimates of maternal mortalityWe greatly welcome the heightened attention to maternal mortality estimates catalysed by the publication by Margaret Hogan and colleagues (May 8, p 1609).1 We applaud the authors for bringing new modelling techniques to bear on mortality data from all over the world. This work not only delivers some welcome “good news”—global reductions in maternal mortality—but also stimulates debate about models and methods which advance the science of measurement. Full-Text PDF New modelled estimates of maternal mortalityThe study on maternal mortality by Margaret Hogan and colleagues1 produced results for the Philippines that we think are quite far from reality. The study estimates that, from 1980 to 1990, the country reduced its maternal mortality ratio (MMR) by 61%—the third largest decline out of 181 countries; and by 81% from 1980 to 2008—the 12th largest. These estimates describe a country with a very successful experience over the past 28 years that merits attention and possible emulation. Full-Text PDF New modelled estimates of maternal mortalityThe article by Margaret Hogan and colleagues1 interested us as researchers at the University of Indonesia who have measured maternal mortality in our country using various methods.2 Although we found the description of the methods and analysis quite difficult to understand, the discussion on how these new estimates differ from the model used previously by Hill and colleagues3 was very helpful. Full-Text PDF New modelled estimates of maternal mortalityMargaret Hogan and colleagues1 estimate maternal mortality for 181 countries by use of a regression model and show that the maternal mortality ratio (MMR) in Burkina Faso in 2008 was 332 deaths per 100 000 livebirths (uncertainty interval 208–522)—a decline from 541 (342–830) in 1980. UN agencies have also used a regression model and estimated the level to be 700 (390–1000) in 2005, falling from 1400 (750–2600) in 1995.2 Although the wide uncertainty intervals of both sets of estimates not surprisingly overlap, we find it hard to believe that differences in the two modelling strategies explain this huge difference in point estimates for Burkina Faso. Full-Text PDF New modelled estimates of maternal mortalityMargaret Hogan and colleagues1 present estimated maternal mortality ratios (MMRs) for Peru of 172 per 100 000 livebirths in 1990, falling to 125 in 2000 and then to 81 in 2008. These are less than the official national data of 265, 183, and 103, respectively.2 The total number of maternal deaths registered by the National Epidemiological Surveillance System has registered a reduction, from 655 in 2000 to 509 in 2008,3 although we know that there is a substantial amount of under-reporting of maternal deaths, estimated to be 46% in 2002 in the last official study published by the National Statistics Institute. Full-Text PDF New modelled estimates of maternal mortalityThe maternal mortality estimates by Margaret Hogan and colleagues1 are an important contribution to the assessment of global progress in reducing maternal mortality. From a developing-country perspective, the value of the estimates varies according to the existence and reliability of vital registration systems. For countries without such systems—ie, those that have to rely on sporadic surveys or censuses—the modelled estimates are the first and probably best source from which to assess trends in maternal mortality since 1980. Full-Text PDF New modelled estimates of maternal mortalityMonitoring progress towards the fifth Millennium Development Goal (MDG) to reduce maternal mortality by 75% is challenging when developing countries lack reliable vital registration systems; consequently estimates from statistical models have been used.1,2 Full-Text PDF