I think your graph actually agrees with what sapphire’s comment was arguing? Among the GWWC pledgers, donations don’t actually hit the pledged 10% of income until well past an income of $100k/​year. It’s hard to eyeball the combined pledger/​non-pledger average donation percentage from the graph, but it seems fair to say it’s under 10% at the vast majority of income levels.
I think your graph actually agrees with what sapphire’s comment was arguing? Among the GWWC pledgers, donations don’t actually hit the pledged 10% of income until well past an income of $100k/​year. It’s hard to eyeball the combined pledger/​non-pledger average donation percentage from the graph, but it seems fair to say it’s under 10% at the vast majority of income levels.