title: A logistic regression model when some events precede treatment: the effect of thrombolytic therapy for acute myocardial infarction on the risk of cardiac arrest.
abstract: When outcomes occur in clinical trials before treatment can be given, neither intent-to-treat nor according-to-protocol analyses give optimal estimates of the treatment effect. A better approach employs a time-dependent variable for treatment. Intent-to-treat analyses are conservative, biasing against treatment; according-to-protocol analyses bias in favor of treatment. We show how to measure the effect of a time-dependent variable in a logistic regression using person-time intervals as units of measurement and describe appropriate methods for reporting model performance. The method is applied to develop a model to predict the probability that a patient with a myocardial infarction will have a sudden cardiac arrest within 48 hours of presentation to emergency medical services both when treated with thrombolysis and when not treated. We use a time-dependent treatment variable because many patients went into cardiac arrest while awaiting treatment. This technique has been programmed into an electrocardiograph for real-time use in an emergency department.
authors.affiliation: Department of Medicine, New England Medical Center, Boston, Massachusetts 02111, USA.
authors.forename: C H
authors.initials: CH
authors.lastname: Schmid
authors.forename: R B
authors.initials: RB
authors.lastname: D'Agostino
authors.forename: J L
authors.initials: JL
authors.lastname: Griffith
authors.forename: J R
authors.initials: JR
authors.lastname: Beshansky
authors.forename: H P
authors.initials: HP
authors.lastname: Selker
mesh_terms: D000368:Aged; D002986:Clinical Trials as Topic; D004812:Epidemiologic Methods; D006323:Heart Arrest / Q000453:epidemiology* / Q000209:etiology; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D009203:Myocardial Infarction / Q000188:drug therapy*; D011336:Probability; D012044:Regression Analysis; D012307:Risk Factors; D015912:Thrombolytic Therapy