Article #10
1998
 
 
 
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Why Do Doctors Disagree When the Evidence is Clear? - Physicians' Judgments of the Outcomes of Therapy for Patients with Heart Failure

Roy M. Poses, Providence, RI
Maria Woloshynowych, London, United Kingdom
D. Mark Chaput de Saintonge, London, United Kingdom

Physicians vary in their use of treatments and frequently fail to use specific treatments despite strong evidence supporting their use. For example, several studies have shown that physicians do not prescribe angiotensin converting enzyme inhibitor (ACEI) drugs for many patients with chronic congestive heart failure (CHF) and systolic dysfunction, a clinical syndrome characterized by the inability of the heart to pump blood adequately for the body's needs, despite data from several large controlled trials that ACEI's prolong survival and decrease morbidity for such patients while causing few adverse reactions. The reasons physicians fail to do what they apparently ought to do in this situation remain unclear. We postulated that physicians may base treatment decisions on their judgments of the probability of relevant outcomes conditional on whether or not the treatment were to be given, and that problems they have judging these probabilities may partially explain practice variation and failure to use treatments supported by evidence. For example, physicians may base decisions to prescribe ACEI's on the difference between their judgments of the probability of survival were ACEI's given and those of survival were ACEI's withheld (the difference is the judged survival advantage due to ACEI's), and on their judgments of the probability of adverse drug reactions (ADR's) were the drugs to be given. Further, physicians' judgments of these outcome probabilities for particular patients may not be based on clinical factors that evidence suggests predicts these rates, and also may be based on factors that might plausibly appear to be predictive, but in fact are not. The purpose of the current study was therefore to assess physicians' judgments and decisions about ACEI use for patients with CHF and systolic dysfunction.

Our physician subjects were 20 general practitioners, 21 hospital-based internists other than cardiologists, and 19 hospital-based cardiologists practicing in London, England, selected essentially randomly. We used a standardized written instrument to assess: the physicians' general propensity to treat patients with moderate or severe CHF with systolic dysfunction (measured as the proportion of 100 such patients they would treat); and their judgments of the overall rates of survival were these patients to be treated or not treated with ACEI's, and of the overall rates of ADR's and serious or fatal ADR's were these patients to be treated with ACEI's. We then asked the physicians to consider 27 case vignettes. The vignettes were constructed such that selected clinical characteristics systematically varied across them. These included characteristics that evidence suggests predict either good or bad outcomes for CHF patients conditional on treatment (e.g., class IV CHF predicts a greater survival advantage due to ACEI treatment, while hypotension predicts a higher likelihood of ADR), and characteristics which do not predict such outcomes (e.g., a history of a kidney stone or of gastroesophageal reflux, or low but normal blood pressure). These latter variables were chosen to represent mild co-morbidity which should not affect outcomes for CHF treated by ACEI's, or because they somehow resembled factors which were predictive, but were not themselves predictive.

We found that doctors' overall propensity to treat with ACEI's was very high and showed little variability across physicians. However, there was little agreement between individual physician's stated propensity to treat patients with either mild-to-moderate or severe CHF and the rate he or she treated corresponding case vignettes. For the majority of physicians, we found relationships both between judged survival advantage due to ACEI's and ACEI decisions for the case vignettes, and between judgments of ADR probability and these treatment decisions.

How physicians weighted clinical variables when making judgments of outcome rates varied widely. The majority of physicians failed to use the severity of heart failure (in terms of the patient's functional status) as a predictor of survival advantage despite strong evidence that patients with the worst functional status have the greatest survival advantage. Some physicians thought mild, irrelevant co-morbidities like a history of a kidney or gastro-esophageal reflux predicted ADR's. Twenty percent (12/60) of physicians used at least one positively predictive or non-predictive variable as a significant negative predictor of survival advantage, and the same proportion of physicians used at least one non-predictive variable as a significant positive predictor of ADR risk.

In summary, asking physicians about their general propensity to treat may reflect an ideal but not their actual treatment decisions. Judgments of relevant outcome rates may relate to and perhaps determine how doctors make decisions in some cases. When judging outcome rates, physicians may fail to take into account predictive variables and/or take into account non-predictive variables. Appreciating how doctors make judgments and decisions may lead to better interventions to decrease unnecessary practice variation and improve quality.

Contact the authors: Roy M. Poses, Maria Woloshynowych, and D. Mark Chaput de Saintonge

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