Analytic Principles in Assessing the Effectiveness of Clinical Preventive Services

Abstract

How effective is clinical preventive medicine? Do screening tests result in more good than harm? Should a vaccine be administered routinely? Is counseling to change modifiable risk factors worth the effort? The Canadian Task Force on the Periodic Health Examination and the US Preventive Services Task Force have attempted to answer these and similar questions by reviewing the quality of the evidence that such maneuvers are effective. Both groups recognized that the performance characteristics of preventive services must be evaluated systematically and impartially if sound clinical practice recommendations are to emerge from the process. Both groups, in developing a methodology and putting it into practice, have developed a better understanding of the analytic principles of assessing clinical efficacy and effectiveness. Although a complete discussion of these concepts is clearly beyond the scope of this book, certain observations regarding the analytic process of evaluating preventive services are relevant to the chapters that follow.

For readers not steeped in the discipline of epidemiology, it can be easy, in all innocence, to overlook factors that may tip the balance of the benefit:harm ratio in either direction. Critical assessment of any screening procedure or preventive maneuver requires scrupulous accounting of all the variables. Dr Woolf’s discussion helps us ask the right questions and identifies the “fudge factors” that may mislead the unwary.