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In this Series paper, we describe the frequency of, trends in, determinants of, and inequalities in caesarean section (CS) use, globally, regionally, and in selected countries. On the basis of data from 169 countries that include 98·4% of the world's births, we estimate that 29·7 million (21·1%, 95% uncertainty interval 19·9-22·4) births occurred through CS in 2015, which was almost double the number of births by this method in 2000 (16·0 million [12·1%, 10·9-13·3] births). CS use in 2015 was up to ten times more frequent in the Latin America and Caribbean region, where it was used in 44·3% (41·3-47·4) of births, than in the west and central Africa region, where it was used in 4·1% (3·6-4·6) of births. The global and regional increases in CS use were driven both by an increasing proportion of births occurring in health facilities (accounting for 66·5% of the global increase) and increases in CS use within health facilities (33·5%), with considerable variation between regions. Based on the most recent data available for each country, 15% of births in 106 (63%) of 169 countries were by CS, whereas 47 (28%) countries showed CS use in less than 10% of births. National CS use varied from 0·6% in South Sudan to 58·1% in the Dominican Republic. Within-country disparities in CS use were also very large: CS use was almost five times more frequent in births in the richest versus the poorest quintiles in low-income and middle-income countries; markedly high CS use was observed among low obstetric risk births, especially among more educated women in, for example, Brazil and China; and CS use was 1·6 times more frequent in private facilities than in public facilities.

Summary Building upon the successes of Countdown to 2015, Countdown to 2030 aims to support the monitoring and measurement of women's, children's, and adolescents' health in the 81 countries that account for 95% of maternal and 90% of all child deaths worldwide. To achieve the Sustainable Development Goals by 2030, the rate of decline in prevalence of maternal and child mortality, stillbirths, and stunting among children younger than 5 years of age needs to accelerate considerably compared with progress since 2000. Such accelerations are only possible with a rapid scale-up of effective interventions to all population groups within countries (particularly in countries with the highest mortality and in those affected by conflict), supported by improvements in underlying socioeconomic conditions, including women's empowerment. Three main conclusions emerge from our analysis of intervention coverage, equity, and drivers of reproductive, maternal, newborn, and child health (RMNCH) in the 81 Countdown countries. First, even though strong progress was made in the coverage of many essential RMNCH interventions during the past decade, many countries are still a long way from universal coverage for most essential interventions. Furthermore, a growing body of evidence suggests that available services in many countries are of poor quality, limiting the potential effect on RMNCH outcomes. Second, within-country inequalities in intervention coverage are reducing in most countries (and are now almost non-existent in a few countries), but the pace is too slow. Third, health-sector (eg, weak country health systems) and non-health-sector drivers (eg, conflict settings) are major impediments to delivering high-quality services to all populations. Although more data for RMNCH interventions are available now, major data gaps still preclude the use of evidence to drive decision making and accountability. Countdown to 2030 is investing in improvements in measurement in several areas, such as quality of care and effective coverage, nutrition programmes, adolescent health, early childhood development, and evidence for conflict settings, and is prioritising its regional networks to enhance local analytic capacity and evidence for RMNCH.

Relative measures of association, such as hazard ratio, odds ratio, and risk ratio, are often used to convey comparative information in medicine and public health. Graphical presentation of such ratios is common practice in technical papers. However, there are two crucial features that must be taken into account when presenting ratios in graphical format: (1) the baseline value for a ratio is 1; and (2) ratios are expressed on a logarithmic rather than arithmetic scale. Szklo and Nieto have nicely summarised these two conditions using three examples of ratios with values of 0·5 and 2·0 (fi gure). Part A uses a baseline of zero and an arithmetic scale. The visual impression given is that the risk ratio of 2·0 is four times larger than the ratio of 0·5. Part B is correct in using a baseline of 1 but wrong in using an arithmetic scale, which gives the impression that the ratio of 2·0 is twice that of the ratio 0·5. In reality, risk ratios of 2·0 and 0·5 are identical in magnitude but work in opposite directions. Part C shows the correct presentation, using a baseline of 1 and a logarithmic scale. We reviewed the 2008 issues of several peer-reviewed general medical journals: the British Medical Journal (BMJ), the Journal of the American Medical Association (JAMA), The Lancet, and the New England Journal of Medicine (NEJM). Inclusion criteria were articles (original, special, or review) that included graphical representation of any relative measure of association. There were 132 articles in total, most of which used forest plots to visualise relative measures of association. Of this total, 46 (35%) used graphs that failed to meet at least one of the above-mentioned conditions. How ever, there were signifi cant diff erences between the four journals. Of the 29 JAMA articles reviewed, none failed to meet the quality criteria and all presented the data correctly. Of the 23 BMJ articles, four did not meet correct representation standards. On the other hand, in both The Lancet and the NEJM, more than half the articles had incorrect representation (22 of 41 articles in The Lancet and 20 of 39 in the NEJM). As Tufte has observed, the purpose of graphics is to “reveal data”, but they must “avoid distorting what the data have to say”. Perhaps it is time for peer-reviewed journals to include among their reviewers experts in graphical present ation alongside statisticians and epidemiologists.