These true gender differences (and differences associated with gender, e.g., weight) have implications for the design of clinical trials, the subset of clinical studies that provides the most rigorous and reliable test of the effectiveness and safety of new drugs and treatments. For example, greater heterogeneity among research subjects may permit the investigator to spot trends that might otherwise be missed, even if the numbers are too small for statistically reliable subgroup analysis. At the same time, greater homogeneity among research subjects reduces unexplained variance.

EVIDENCE OF GENDER DIFFERENCES

This report, originating as it does from concerns about insufficient attention being directed toward identifying and understanding gender differences, of necessity highlights diseases and treatments that can differ by gender in a variety of ways. Differences can arise from a range of factors, both biological (e.g., the effect of endogenous or exogenous hormones or gender-related differences in body mass, etc.) and psychosocial (e.g., gender-related differences in behaviors such as smoking or substance abuse). The question that must be addressed is to what extent are gender differences per se clinically meaningful in the treatment of conditions involving both genders?

Most clinical researchers and clinicians would argue that women and men do not respond significantly differently to the presence of disease or the effect of treatment. Even for diseases where women and men differ significantly in the likely time of onset (such as heart disease), they will usually respond in much the same way to treatment and experience a similar evolution of the disease. The underlying reasons for this belief are rooted in several observations regarding health problems relevant to both men and women: for the majority of drug treatments, efficacy and safety do not depend on such factors as body mass, adipose tissue, hormones, or other factors associated with gender. Treatments by surgical procedure for diseases associated with both genders seldom differ because the patient is a woman instead of a man; and to the extent that women may be treated differently, it is because of factors associated with gender but not specific to gender, such as bone mass or organ size. Finally, a long history of nonhuman research—ranging from work with bacteria to research with mammals—supports the conclusion that subgroup differences are rare. Most treatments and disease processes are thus thought to be insensitive to gender per se. Nevertheless, the evidentiary base for quantifying these claims in humans is weak because the relevant data have not been organized into an accessible format and the claim is seldom questioned.

At the same time, concern is mounting among both scientific observers and lay representatives that researchers and clinicians may be too quick to



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