Usually researchers want to avoid people dropping out of their experiments. The wicked brilliance of this experimental design is that the dropout rate is precisely what the experimenters wanted to study.
Unsurprisingly, the experiment found that people will do more work when you pay them a better rate, and they will do less work when you show them annoying adverts. Comparing the two lets the researchers estimate the magnitude of the effect, which is striking: removing the annoying adverts entirely produced as much extra effort as paying an additional $1.15 per 1,000 emails categorised — and effectively $1.15 per 1,000 adverts viewed. But $1.15 per 1,000 views is actually a higher rate than many annoying advertisers will pay — the rate for a cheap advert may be as low as 25 cents per 1,000 views, says Goldstein.The rest here.
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Good adverts are much less destructive. They push workers to quit at an implicit rate of $0.38 per 1,000 views, for an advert that may pay $2 per 1,000 views to the publisher.