Eyeballing the chart, it seems like more than a “years since pledge” dependence, there’s a “actual year” dependence independent of the pledge year, at least after year 0. The most stark change is from 2010 to 2011, when reporting rates increased significantly for both of the first two cohorts. I’m guessing that this is due to some technicality rather than an actual behavior change. There also seems to be a significant decay across all cohorts from 2015 to 2016 that would likely be even more obvious if plotted. Maybe this also has a boring explanation, or maybe it has to do with identifiable events in 2016.
Eyeballing the chart, it seems like more than a “years since pledge” dependence, there’s a “actual year” dependence independent of the pledge year, at least after year 0. The most stark change is from 2010 to 2011, when reporting rates increased significantly for both of the first two cohorts. I’m guessing that this is due to some technicality rather than an actual behavior change. There also seems to be a significant decay across all cohorts from 2015 to 2016 that would likely be even more obvious if plotted. Maybe this also has a boring explanation, or maybe it has to do with identifiable events in 2016.