You haven't lived until you've called total strangers on a Saturday evening to ask them if they've had diarrhea in the past six weeks.
I volunteered to do four hours of phone calling this weekend as part of an epidemiologic study. It was an interesting experience. I am feeling much, much more sympathetic towards telemarketers at the moment. Some people slam the phone down really hard, and I think my ears are still ringing from the times the number I dialed connected with a fax machine. That is a truly horrible noise.
I will say that everyone who took enough time to listen long enough to understand why I was calling was happy to cooperate. If I managed to get past "Hello. My name is Nan and I'm calling from Large Nameless Agency . . . " people did stay on the line and answer the questions.
It did occur to me that not many people must bother checking caller ID before picking up the phone. I was cold calling people in a deeply red state, and the name that would have been showing on caller ID was US Government. I'm a federal employee, and even I would hesitate to take a call from Uncle Sam on a Saturday night.