Alexander M. Walker

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BACKGROUND Although animal studies have raised the possibility that prolactin-elevating dopamine antagonists used to treat psychotic disorders may initiate and promote breast cancers, epidemiologic studies in humans have been limited and inconsistent. METHODS A retrospective cohort study was conducted of 52 819 women exposed and 55 289 not exposed to(More)
Multilayer neural networks have been faulted for functioning as "black boxes" and for failing to assess the relative importance of the input factors. The aim of this paper is to illustrate how neural networks can classify individuals. The authors investigated the role of weights in the formation of neural networks' decision surfaces and decision regions.(More)
Observational studies often provide the only available information about treatment effects. Control of confounding, however, remains challenging. The authors compared five methods for evaluating the effect of tissue plasminogen activator on death among 6,269 ischemic stroke patients registered in a German stroke registry: multivariable logistic regression,(More)
Periconceptional folic acid supplementation reduces the risk of neural tube defects (NTDs). To determine whether periconceptional exposure to folic acid antagonists (FAAs) might therefore increase the risk of NTDs, the authors examined data from an ongoing case-control study of birth defects (1979-1998) in the United States and Canada. They compared data on(More)
BACKGROUND In observational research, propensity score techniques can be used to account for baseline differences between compared therapies. Although propensity scores are used increasingly often, their limitations in settings without complete data may not be recognized. OBJECTIVES We sought to evaluate the ability of propensity score matching to(More)
The authors developed and cross-validated prediction models for newly diagnosed cases of liver disorders by using logistic regression and neural networks. Computerized files of health care encounters from the Fallon Community Health Plan were used to identify 1,674 subjects who had had liver-related health services between July 1, 1992, and June 30, 1993. A(More)
PURPOSE To describe how computer-assisted presentation of case data can lead experts to infer machine-implementable rules for case definition in electronic health records. As an illustration the technique has been applied to obtain a definition of acute liver dysfunction (ALD) in persons with inflammatory bowel disease (IBD). METHODS The technique(More)
In the conduct of case-control studies, it has been a general experience that some cases are identified only after death, and that others cannot be personally interviewed because of extreme morbidity. As a way of dealing with the dilemma of obtaining data on unavailable cases, investigators have sometimes chosen to interview a relative or friend (a proxy(More)
The gait scoring system developed by Manson and Leaver was used by five experienced observers to assess the gait of 83 milking Holstein-Friesian cows in a live recording session, and video recordings were made. The agreement between the scores of the observers at the live session, and between each observer's scores at the live session and a video session,(More)
BACKGROUND We sought to quantify the impact of patient characteristics on complications and health care costs associated with influenza and influenza-like illness (ILI) in a nonelderly population. METHODS Patients with medical reimbursement claims for influenza in the 1996-1997 season were identified from the automated database of a large private New(More)