After a discussion I would like to clarify one thing ~ that even Level 1 studies can contain bias. But the evidence is of higher quality than any other study level. For example if someone wants to bring forth a prospective controlled study comparing the side effects of brachytherapy to a placebo in the treatment of prostate cancer the placebo will have superior performance in the way of side effects but what's the point? You haven't shown improved performance against prostate cancer. But the study will overwhelmingly support that placebo has far fewer side effects. This would not be a quality study for disease control. It's a rather useless Level 1 study.
The US Preventive Services Task Force sets the following guidelines is assessing study quality:
1. Do the studies have the appropriate research design to answer the key question(s)?
2. To what extent are the existing studies of high quality? (i.e., what is the internal validity?)
3. To what extent are the results of the studies generalizable to the general U.S. primary care population and situation? (i.e., what is the external validity?)
4. How many studies have been conducted that address the key question(s)? How large are the studies? (i.e., what is the precision of the evidence?)
5. How consistent are the results of the studies?
6. Are there additional factors that assist us in drawing conclusions (e.g., presence or absence of dose-response effects, fit within a biologic model)?
The following link provides how quality is determined after a study and/or how a study will be rated after it's completed...www.uspreventiveservicestaskforce.org/uspstf07/methods/benefit.htm
As you can see it's a complicated process. But if you are going to use studies to make points or to make decisions, you should at least try to understand this process in which a study goes through.
Educating yourself goes a long way...
Advanced Prostate Cancer at age 44 (I am 49 now)
pT3b,N0,Mx (original PSA was 19.8) EPE, PM, SVI. Gleason 4+3=7
Da Vinci Surgery ~ 2/16/2007
Adjuvant Radiation Therapy ~ IMRT Completed 8/07
Adjuvant Hormone Therapy ~ 28 months on Casodex and Lupron.