16 – Effects of Age and Gender

Age and gender are important variables relevant to the design and analysis of many clinical studies. Aging is accompanied by physiologic changes that alter host responses to surgical illness, changing patterns of disease (e.g., a preponderance of perforated vs. nonperforated appendicitis), changing disease frequency (e.g., increased incidence of many types of cancer), and greater morbidity and mortality following surgery, trauma, and critical illness. Gender-dependent differences in clinical outcomes from trauma, sepsis, and other conditions have been identified in a number of studies, although such findings are not universal or fully consistent. However, they are nonspecific descriptors in that they convey a range of biological, cultural and other influences, and are surrogates for other variables. The investigator must focus and formulate the research question carefully with this in mind. When age or gender is the primary variable, human studies are necessarily observational, because randomization on age and gender are not feasible. Descriptive and prognostic analyses of such studies are straightforward; establishing causal inferences requires careful study design and planning of the statistical analysis.