Thanks for your interest, Dale, and Owen for responding so thoroughly.
I overall agree that there is a lot of information it would be nice to get at, although the numbers are somewhat small if we’re trying to work out the difference between, say, the 2009 cohort and the others (since there were only around 30 members in 2009). Now that I can spend less time on fundraising, I’ll try to put together a post about this.
Just to add a couple of points to what Owen has said: On the question of students to earning—that was definitely a time we were worried people would drop out. The data doesn’t seem to suggest that’s the case though—so far it seems that people do tend to actually start giving 10% when they start earning.
On the verifying donations—we have in the past compared AMF’s data on donors with member self-reporting. While the self-reporting was far from perfect, people were at least as often under-reporting as over-reporting. (And most often discrepancies simply turned out to be mistakes about when the person had donated.) For the reasons Owen mentions, we did this once (to get a sense of whether reporting was approx accurate) but we aren’t planning to do it again.
On the 2009 cohort—would it make sense to bucket this with the 2010 cohort? (So treating the first 14 months of GWWC as one cohort, and in years thereafter)