@article{ref1,
title="Implications of alternative sampling strategies for emergency medical service evaluation",
journal="Medical care",
year="1979",
author="Mitchell, J. B. and Pozen, M. W. and D'Agostino, Ralph B. and Berezin, M. M.",
volume="17",
number="8",
pages="828-834",
abstract="Evaluations of emergency medical service (EMS) programs have been ambiguous, due in part, to problems of sample definition. Four different sampling strategies were studied: 1) all patients in cardiac arrest; 2) patients with a final diagnosis of myocardial infarction (MI); 3) patients with an emergency room diagnosis of &quot;rule out MI&quot;; and 4) patients identified by the ambulance team as a possible MI. Using a regional data base of all ambulance runs, we created study samples based on each of these strategies and measured the error that may be introduced as a result of sample selection. Bias was measured along three parameters of EMS system performance: 1) observed incidence of MI in the ambulance system; 2) condition recognition--the ability of the ambulance team to correctly identify acute cardiac patients; and 3) emergency room and hospital mortality rates. The emergency room diagnosis strategy systematically excludes all false-positives, while samples based on the ambulance team's assessment omit all false-negatives. The final diagnosis strategy yields significant underestimates of cardiac mortality. Samples restricted to cardiac arrests result in biased estimates of both the incidence of MI and the number of deaths.<p /><p>Language: en</p>",
language="en",
issn="0025-7079",
doi="",
url="http://dx.doi.org/"
}