VOLUME 54 | NUMBER 3 | JUNE 2019
Instrumental variables: The power of wishful thinking vs the confounded reality of comparative effectiveness research
Keele and Small responded to our article on instrumental variables (IVs) published in Health Services Research in February 2017.1, 2 Here, we address their efforts to defend IVs and we present additional evidence of the unreliability of IVs in comparative effectiveness research (CER). We appreciate that some economists, statisticians, and other IV adherents are emboldened by their faith in the power of weak crosssectional associations to accurately reflect the world. But health outcomes research requires confronting the interrelatedness of social and medical factors—almost always a confounded reality with unmeasured and, indeed, unknown variables.3 That is, most IV studies assume life is far less confounded than it is..
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