In Survival Mode (Endless), do the zombies on each wave vary

plants-vs-zombies

Is the type and number of attacking zombies in each wave predetermined? Or does it vary depending on factors such as how many plants I've got in the ground, what strength these plants are, or how much Sun I've saved?

Best Answer

I've played dozens of rounds and zombies definitely vary, but as I use very similar strategy each time it makes me think that the variation is rather random.