As usual, XKCD has the relevant joke: http://xkcd.com/925/
But yeah, when you have the following paragraph in a paper:
"Some may argue that our results only reflect screening and treatment patterns for prostate cancer, with the more developed countries having both a higher use of OCs and a higher incidence of prostate cancer. Unfortunately data on worldwide screening tendencies or prostate specific antigen (PSA) use is unavailable. However, we included a multivariable analysis... "
You're a SCIENTIST. If data does not exist, you go out and generate it. That's WHAT WE DO. I understand it's not practically possible given limited funds and time to gather all the data that would make your story complete. However, when you're essentially saying "There's a giant whole in this story, but plugging it would take too much effort, and only some of you are going to call us on it, so we'll just see if we can skate by with a half-assed " mulitvariable analysis' " it really does say that your paper shouldn't have been published to begin with.