Pawel Sobkowicz writes:
How many zombies do you know?’ Using indirect survey methods to measure alien attacks and outbreaks of the undead, Arxiv preprint arXiv:1003.6087, 2010
I hope you would find interesting the following paper, recently posted on arXiv:
Aliens on Earth. Are reports of close encounters correct?, arXiv:1203.6805
This is soooooo much better than getting links to bad graphs or to papers on sex ratios!