Confounding A confounder is a known risk factor for the disease and is associated with the exposure. The confounder may account for the apparent effect of the exposure on the disease or mask a true association. Confounders have unequal distributions between the study groups.
Age, race, and socioeconomic status are potential confounders in many studies. Results may be adjusted for these variables by using statistical techniques such as stratification or multivariable analysis. Adjusting for confounding variables aids in understanding the association between the outcome and exposure if the confounding variable were constant.
Multivariable analysis is a statistical technique commonly used in epidemiologic studies that simultaneously controls a number of confounding variables. The results from an adjusted analysis include the adjusted odds ratio or relative risk that reﬂects an association between the exposure and the outcome and accounts for the specific known confounders that were included in the analysis.
The criteria needed to establish a causal relationship between two factors, especially exposure and disease, are defined (11). Although there are nine separate criteria for judging whether an association is likely to be causal, several of these criteria are most relevant for clinical studies.
Biologic gradient or dose response refers to a relationship between exposure and outcome such that a change in the duration, amount, or intensity of the exposure is associated with a corresponding increase or decrease in disease risk.
Plausibility refers to knowledge of the pathologic process of the disease or biologic effects of the exposure that would reasonably support an association. Plausibility overlaps with another concept, coherence, which also refers to compatibility with the known biology of the disease.
Experiment refers to the evidence that the disease or outcome can be prevented or improved by an experiment that eliminates, reduces, or otherwise counters the exposure.
Consistency refers to whether the association was repeatedly observed by different investigators, in different locations and circumstances.
Temporality refers to the concept that cause must precede effect. For example, is it possible in a case-control study that symptoms of preclinical disease could lead to the exposure? Investigators must demonstrate that the exposure was present before the disease developed.
Strength refers to the strength of association. The further the deviation of the relative risk or odds ratio from 1, the stronger the association and the easier it is to accept that the study results are real. For example, studies have shown that the possession of a BRCA mutation may increase the lifetime risk for ovarian or breast cancer some 30-fold. Although strength is a very important criterion, large-scale genetic studies suggest that other factors are equally important. For example, multiple studies reported several variants at the 8q24 chromosomal region associated with prostate and other cancers (12). Even though possession of one allele may change risk by only about 15% (i.e., OR = 1.15), the consistency and high statistical significance suggest the association cannot be caused by chance and this is considered a true association.
Reviewing the medical literature is part of the ongoing education for those who provide clinical care. Incorporating research findings into clinical care is enhanced by understanding different study designs, their strengths and weaknesses, and the measures of association they are able to provide. Evaluating whether there is enough evidence available to support changing a specific medication, procedure, or protocol used to care for patients is the cornerstone to improving clinical practice. In a field that is rapidly progressing, understanding clinical research helps physicians provide optimal care for the women they treat everyday.
Eric R. Sokol Rene Genadry Jean R. Anderson
Although the basic facts of anatomy do not change, our understanding of specific anatomic relationships and the development of new clinical and surgical correlations continue to evolve.
There is significant variation in the branching pattern of pelvic blood vessels between individuals, and patterns of blood ﬂow may be asymmetric from side to side in the same individual. The pelvic surgeon should be prepared for deviations from “textbook” vascular patterns.
An understanding of the development of pelvic ﬂoor disorders and their safe and effective management requires a comprehensive knowledge of the interrelationships between the bony pelvis and its ligaments, pelvic muscles and fasciae, nerves and blood vessels, and pelvic viscera.