@article {11546,
	title = {Assessing the Effect of an influenza vaccine in an Encouragement Design},
	journal = {Biostatistics},
	volume = {1},
	number = {1},
	year = {2000},
	pages = {69-88},
	author = {Guido Imbens and Keisuke Hirano and Donald Rubin and Xiao-Hua Zhou}
}
