a razz odds question

[appears]

I've read in more than one place that the odds of outdrawing a single opponent on 4th st. is 4-1 . Can someone show me the math? I can't seem to come up with that number. Also, if this number is correct, does this mean that on any given street, if you are getting 4-1 pot odds, you need to be calling if you feel you are at most only one card behind? Two examples : 1) defending the bring-in against a single opponent showing a baby upcard when you have a hand like A2/K ; 2) you have caught bad on fourth while your opponent appears to have caught good ... say A2/72 v xx/A2 . (Assume in both examples that the cards that are out don't have any particular sway.)

I also guess it's worth mentioning that I read through this whole lengthy post on defending the bring-in but wasn't exactly sure what to draw from its conclusions. I assume that the odds of outdrawing someone on 4th st. are pretty relevant to answering that question. But I'll hold off on any follow-up questions until someone responds and sets me on the right path.