Oo, oo, let me jump in before the thread locks...

World War Z introduces the critical survival mechanism imo - zombies eventually rot away. The math study doesn't account for this with a time element in their equations - if all you have to do is outlast zombies, its simply a matter of provision and protection for t amount of time, something simple like

survival = x(t) provisions + y(t) protection - rnd odds of failure of x / y

Safest place - an unscaleable elevation, with a cache of food and water for the duration.

If a zombie rots, he is not your enemy - avoid him, they will eventually go away. I wish I could remember the quote exactly, probably Henry the II:

"He has launched the arrow, and the safest path is to avoid its aim."