The link below is an actual, legitimate academic study performed by the University of Ottowa and Carleton University, and published in 2009. They aren't saying they think zombies are real, it was more of an exercise in predicting the spread of real infectious diseases. They thought zombies would be an extreme, and interesting, example of how rapidly a disease can become a global problem.

They cite Max Brooks, George Romero, Simon Pegg (Shaun of the Dead), 28 Days Later, and Resident Evil. They use Brooks' rules, more or less, and assume that there is a short time between the bite and the time of the bitten person's death and reanimation (unless of course the person dies of their injuries sooner, like Amy having her jugular vein torn out and bleeding to death). The zombies are assumed to be slow and stupid, and they can be killed by massive brain trauma or decapitation.

They charted two things - the population of "Susceptibles" (uninfected, living humans) and the population of "Zombies". Susceptibles who die of non-zombie related causes do not become zombies, unless they are infected before dying. All susceptibles killed by zombies do become zombies, as do all people attacked and infected by zombies before dying of other causes.

They then charted these 2 figures in each of several possible scenarios.

1) Basic Model - Conditions are as described above, with no organized response from gov't or military. All humans are eradicated very quickly. The same model was also run with a 24 hour latent period between the time of infection and the time of death/reanimation; this slightly delayed the total eradication of humans.

2) Model with Quarantine - In this model, a partial quarantine is attempted. Only infected and zombies are put under quarantine, and once they are inside the quarantine zone, it is impossible to escape without being killed. Any zombies and infected who did NOT attempt to escape would NOT be destroyed, only isolated forever. However, large numbers of infected and zombies will never be caught and put in quarantine due to the resources, manpower, and time needed to do so. Again, this only manages to delay the total eradication of humans very slightly.

3) Model with Treatment - This model assumes that a 'cure' for zombie-ism quickly becomes available, and can somehow return the zombie being cured to its original, human form. However, upon becoming human again, the cured person also becomes susceptible to infection again. In this model, humans were not completely eradicated, but would be reduced to a tiny fraction of our original population and totally outnumbered by zombies, who we will have to coexist with forever.

4) Model with "Impulsive Eradication" - This basically means we try to kill as many zombies as possible in coordinated attacks as often as possible, whenever enough men and resources can be pooled to do so - and gathering the necessary men and material will be difficult or even impossible. In this model, humanity only survives if the attacks are sufficiently strong and frequent, and only if each new attack kills far more zombies than the last one did.


They sum it up better than I can, so here is a quote from the "Discussion" section.

"...These results assumed that the timescale of the outbreak was short, so that
the natural birth and death rates could be ignored. If the timescale of the outbreak increases, then the result is the doomsday scenario: an outbreak of zombies will result in the collapse of civilisation, with every human infected, or dead. This is because human births and deaths will provide the undead with a limitless supply of new bodies to infect, resurrect and convert. Thus, if zombies arrive, we must act quickly and decisively to eradicate them before they eradicate us."

And finally, here is the actual link to the report in PDF format.

WHEN ZOMBIES ATTACK!: MATHEMATICAL
MODELLING OF AN OUTBREAK OF ZOMBIE
INFECTION

 

Credit to Philip Munz, Ioan Hudea, Joe Imad, & Robert J. Smith
School of Mathematics and Statistics, Carleton University
Department of Mathematics and Faculty of Medicine, The University of Ottawa