GOOD TECHNOLOGIES GONE BAD - HOW AND WHY THE COST-EFFECTIVENESS OF A MEDICAL INTERVENTION CHANGES FOR DIFFERENT POPULATIONS

Cost-effectiveness (CE) ratios vary considerably, not only across inte rventions, but within single interventions. Using a simple decision-tr ee model of the treat-vs no-treat decision to organize the analysis, f our potential errors leading to these within-treatment differences in CE ratios are identified. These errors arise from estimates relating t o 1) prior probabilities of disease; 2) treatment. efficacies; 3) cost s of treatment; and 4) patient preferences. Systematic biases, where p resent, suggest overuse of medical interventions. For diagnostic tests , two additional potential sources of error are considered (using a si mple decision tree incorporating both test and treat decisions). These involve 5) sensitivity and specificity of the diagnostic test and 6) inappropriate choice of ''cutoff' to determine abnormal patients, in p art arising from errors in estimating prior probability of disease.