Email is a horrible method of communication, and one of the things it’s horrible at is getting people to do things. This is the price to pay for how convenient it is to send an email. No doubt requiring that volunteers make a phone call to offer to volunteer instead would decrease the attrition rate but it’s unclear if you’d actually get more useful work that way.
Is 50% lower than usual? My intuition says the norm is between 15% and 40%, with ~60% confidence.
Givewell’s volunteer failure rate was apparently ~80%: http://blog.givewell.org/2011/07/13/a-good-volunteer-is-hard-to-find/ (LW discussion).
Email is a horrible method of communication, and one of the things it’s horrible at is getting people to do things. This is the price to pay for how convenient it is to send an email. No doubt requiring that volunteers make a phone call to offer to volunteer instead would decrease the attrition rate but it’s unclear if you’d actually get more useful work that way.