Ask participants for their email address in a way that makes it clear they are not required to provide their address and will not be penalized if they do not provide it (i.e., they will still be paid for their screening survey responses even if they do not provide their email address to allow for follow-up).

You may want to use participants' email addresses to send them a link to the follow-up study in cases where the participants aren't doing the screening and the follow-up survey in one sitting. Be sure to seek consent to send the follow-up survey prior to sending it.