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. 2021 Apr 16;4:73. doi: 10.1038/s41746-021-00442-3

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — a The True and False alert rates using different thresholds for classification for alerts raised 1 (violet), 2 (light violet), 3 (dark pink) and 4 (green) weeks ahead. The black curve depicts the overall True and False alert rates. On each curve, the dot shows the True and False Alert rates at 42.5% threshold. For a given threshold (xth percentile of the forecast interval), we defined a True alert for a week where the xth percentile of the forecast interval and the observed incidence for a country were both greater than 0; false alert for a week where the threshold for a country was greater than 0 but the observed incidence for that country was 0; and missed alert for a week where the threshold for a country was 0 but the observed incidence for that country was greater than 0. True alert rate is the ratio of correctly classified true alerts to the total number of true and missed alerts (i.e., (true alerts)/(true alerts + missed alerts)). False alert rate is similarly the ratio of false alerts to the total number of false alerts and weeks of no alert (where the observed and the threshold incidence are both 0). b The True (green), False (orange) and Missed (red) 1 week ahead alerts using the 42.5th percentile of the forecast interval as threshold. The figure only shows countries on the African continent for which either the 42.5th percentile of the predicted incidence or the observed incidence was greater than 0 at least once. The first alert in each country is shown using larger squares. Alerts in a country in a week where there were no observed cases in the previous week are shown using triangles. In each case, weeks for which all observed points were imputed are shown in lighter shades. Country codes, shown on the y-axis, are as follows: CIV Côte d'Ivoire, GHA Ghana, GIN Guinea, LBR Liberia, MLI Mali, NGA Nigeria, SEN Senegal, SLE Sierra Leone, BFA Burkina Faso. The alerts are based on forecasts using ProMED data, a 2-week calibration window and a 4 week forecast horizon.