To Rule Out Confounding Observational Studies of

Authors: David N Fisman

Publish Date: 2007/07/23

Volume: 167, Issue: 14, Pages: 1554-1555

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Abstract

We appreciate the comments of Jackson and colleagues regarding possible residual confounding by health status as an explanation for the protection provided by influenza vaccination against death in our study1 Confounding and biases represent everpresent threats to validity for even the best thoughtout observational research2 We controlled for numerous potential confounders including health status nursing home residence and severity of illness on admission in multivariable models and the observed protective effect of influenza vaccination remained robust Furthermore we included only hospitalized individuals with pneumonia The implicit exclusion of vaccinated individuals at low risk of pneumoniarelated hospitalization makes a “healthy vaccine effect” unlikely

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