@article {gu2007jrssb,
	title = {Measurement error modeling with an approximate instrumental variable},
	journal = {Journal of the Royal Statistical Society, Series B},
	volume = {69},
	year = {2007},
	pages = {797-815},
	doi = {10.1111/j.1467-9868.2007.00611.x},
	author = {Gustafson, P.}
}
