I can't answer whether the confirm email box helps though I suspect it would help some). But if quality of emails is real important, go to the next step beyond just confirming emails and use a form of email validation. If you have some sort of offer (free white paper, etc.), only give the offer when the email is validated (or as part of the validation process - by emailing the item to them).

Thanks for the replies so far.

I'd like to clarify that I'm not interested in sending a confirmation email because that wouldn't work well with our system.

What I'd like to know is if anybody has data showing the actual effect of a "confirm email" field on a registration form.

It might increase the quality of the data submitted, but it might also depress response. Any evidence one way or the other is appreciated.

Improves accuracy - improves quality
It's easy to make a typo...hard to slip by a second time with confirm of email

Confirm email has notified me many times when both didn't match so I knew to fix my entry

Steve,

Thanks for the statistics. That's helpful.

Our online registration process is for the purchase of a product. Collecting the email address is a good thing, but not crucial. We get pretty decent data now, so the question is how far to go to get better data.

Adding any sort of confirmation (e.g., we send an email and they have to click on a link to continue the process) may get us better email names, but it's certain to lose us sales (on the well-known principle that any time you add a step you lose people).

Thanks,

Greg