THE ROLLING BASELINE AND RE-ESTIMATING THE ENTIRE TREND
The methodology we use to estimate the number of additional users of modern methods of contraception has two important components, both of which confer advantages related to data quality and accuracy. The first is the designation of 2012 as the baseline year or starting point for our calculation—the point at which we set the number of additional users at zero. For each reporting period, we compare the total number of users in the current year to the total number of users in the baseline year (2012). The difference between the two totals is the number of additional users.
The second component is the use of a “rolling” baseline, meaning we recalculate annual estimates (starting with 2012) on an ongoing basis as new data become available. Continuously incorporating new data improves our ability to monitor progress, so that by 2020 our estimates for all years (2012 to 2020) will represent the most comprehensive and accurate data available. Calculations of the number of additional users depend on mCPR and the population of women of reproductive age (WRA). There is often a lag time of a year, and sometimes longer, before the surveys used to calculate mCPR are released. In addition, updated population estimates (including WRA) often include retrospective modifications of past estimates based on newly released census data and other sources.
Consequently, as new data become available, they affect not only current year estimates but those calculated in previous years as well. The advantage of using rolling estimates is seen by comparing the estimate of the number of users of modern contraception that was calculated for the London Summit on Family Planning in 2012 (258 million) to the updated estimate for 2012 that we use now (270 million).
Our new baseline calculation incorporates new surveys that give us a better sense of the current mCPR in a country as well as what the mCPR was in 2012. In addition, our new baseline calculation takes into account updated UN Population Division estimates that were released in 2015 and affect the number of women of reproductive age in 2012 and today. As a result we now consider the total number of contraceptive users in 2012 to be 12 million more than originally estimated in 2012. Were we to use the old estimate for 2012, this discrepancy could be misconstrued as 12 million additional users on top of the actual 30.2 million additional users.
Not only is our 2012 estimate updated, but so are our 2013 and 2014 estimates. This means that the number of additional users that we estimated for these years in our last report has also been re-estimated. Because of these changes, it is important not to compare numbers in this report to numbers in previous reports. Instead, this report publishes the entire 2012 to 2016 trend based on the most recent data, enabling comparison of changes over time. More information on the methodology for the rolling baseline can be found in a Track20 technical brief.25
New data from surveys and service statistics become available over the course of the year, and 17 countries have new data available since last year’s report. Due to variations in data sources, the strength and “recency” (how old the data are) of the estimates differ from indicator to indicator and country to country. The data in this year’s report range in recency from 2006 to 2016 and are classified accordingly in the estimate tables: “very old” (before 2009), “old” (2009–2011) and “recent” (2012 to the present).
USING SERVICE STATISTICS TO IMPROVE ESTIMATES
Track20 uses service statistics to inform mCPR trend estimates for countries where these data meet the following criteria:
- consistent levels of reporting over time (so changes in volume of service statistics do not represent more facilities reporting, rather than an increase in service delivered);
- at least three years of consistent data, with at least one year overlapping with a survey so that the model can calibrate the two trends; and
- at least one year of service statistics reported after the most recent survey; if a survey is the most recent data point, the survey will be used to inform the mCPR trend.
In 2016, mCPR estimates were informed by service statistics for 11 countries.