Obtaining reliable and valid data in general is a difficult undertaking. Information and data collected optimally is both precise (repeatable) and accurate (degree to which a variable represents what it is supposed to represent).
Common meth- odologies to increase precision for studies include the standardization of measurement with an operation manual, training and certification of the observer, refinement of instruments, automation of instruments, and repetition of measurements with value averaging . These techniques ultimately attempt to minimize the role of chance or random error. Similar techniques are used to maximize accuracy, where bias by the subject, observer, or instrument creates systematic errors in the data. Additional techniques utilized in addition to those previously mentioned to maximize precision, include making unobtrusive measurements, instrument calibration, and blinding.
The most common pitfalls to internal validity include the definition of ED, ED measurement, time frame for measurement, patient versus MD recording of data, attrition bias, and the role of chance.
Sexual dysfunction exists as one of the most significant detractors to the quality of life measures in patients treated for localized cancer of the prostate (CAP). A study in 2003 found that even as long as 92 months after radical retropubic prostatectomy (RRP), more than 75% of the treated men were sad or tearful about ED and over 70% felt that the quality of life was adversely affected. ED is an unfortunate consequence that accompanies CAP treatment.
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After an extensive abstraction process, an AUA prostate cancer guideline update panel task force attempted to establish ED prevalence rates after RRP, XRT, and brachytherapy, with non-specific results from 31 articles. The article noted that subcategorization of results according to specific variables was not feasible due to imprecise or absent descriptions of these variables in the original articles. In an attempt to develop a basic source for patients and physicians to look up the likelihood of the developing ED after the various prostate cancer treatments stratified by risk factors that were listed, we summarize the 31 articles previously abstracted in addition to articles commenting on cryotherapy, androgen ablation, and prostate cancer treatment comparison studies.
In selecting these articles, we placed importance on studies with high power, or those that elaborated on important patient factors (age, medical comorbidities, and preoperative erectile status) and those that used consistent ED definitions and validated ED information collection tools. Our experience was similar to that of the AUA task force, finding unacceptably large vari- ance in the data and the quality of study methodology.