Preparing for the evaluation of health information exchange.

To prepare for the evaluation of a health information exchange (HIE) project in New York City, we collected pre-implementation data regarding aspects of care that might be affected by the HIE initiative. The first application of the HIE will be to provide data to emergency physicians; therefore, we focused on measures relevant to emergency care. These data allowed us to better understand the characteristics of our patient population and perform sample size calculations for certain outcome measures.