The causal incrementality of ad spend is rarely negative. You expect to see decreasing returns with additional ad spend. For each dollar in ad spend, one advertiser might want to see $3 in revenue, another $5. Incrementality studies then allow advertisers to tune spend to their operating points.

Facebook does like money. Do you think lying to the biggest advertisers in the world is the best long-term strategy, or do you think instead it might be better to report out the most accurate results possible?