FP2020 seeks to enable an additional 120 million women to use modern contraception by 2020. In order to measure additional users of modern contraception each year, the total number of modern users in each year must be compared to a baseline number of users. For the case of FP2020, the baseline is set to 2012, the year the initiative began. Having an accurate estimate of the number of women who were using modern contraception in 2012 is key to measuring the success of FP2020. A Rolling Baseline allows for more accurate estimates of contraceptive use in 2012.
As more data becomes available each year, we can make better estimates of current contraceptive use, as well as better estimates of past use. Therefore, rather than measuring additional users from the original estimation of modern users across the FP2020 countries in 2012, we recalculate the full trend (starting with 2012) each year using the new and best data available.
We call this concept a “rolling” baseline because we are not using the original baseline figure that was calculated for 2012 in 2012.
There is often a delay of a year or longer before the surveys used to calculate mCPR are released. In addition, updated population estimates (including women of reproductive age (WRA)) often include retrospective modifications of past estimates based on newly released census data and other sources.
New data not only affects current year estimates, but those for prior years as well. For example (see graph), if a 2016 survey is not released until late-2017, the data used for FP2020 calculations would not be available when the 2017 estimates are prepared. This new survey will not only effect the estimate of mCPR in 2016, but, also the trend in in the years leading up to the survey. Using a rolling baseline allow estimates to incorporate new data, ensuring they are the best estimate given all data available.
Continuously incorporating new data improves our ability to monitor progress, so that by the year 2020, our estimates for all years (2012 to 2020) will represent the most comprehensive and accurate data available.
The advantage of using rolling estimates is seen by comparing the original estimate of the number of modern contraception users that was calculated for the London Summit on Family Planning in 2012 (258 million), to the updated estimate for 2012 that we used in the 2017 Progress Report (270.5 million).
Our calculation incorporates new surveys and updated population estimates for 2012 that were not available at the time of the London Summit. As a result of this new information, we now consider the total number of users in 2012 to be nearly 12 million greater than was previously thought. Had we used the old estimate for 2012 as our baseline figure, it would overestimate the number additional users in 2017 by nearly 13 million (see graph).
Our re-estimation of the number of modern users in 2012 changes less each year, as now many countries have at least one post-2012 survey included in their projections. The largest shift in our baseline estimate was in 2013/2014, when many new surveys became available that were not yet published when developing the 2012 London Summit estimates.