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Saturday, January 30, 2010

Blog Updates for January 2010

Jan 22/09. We added to: Bradford Hill Criteria of Causation: In fact there is a mathematical condition known as Cornfield's condition that states that the apparent effect cannot be reversed by the confounder if the effect of the confounding factor is not greater than the effect of the apparent factor. (In the table above where the apparent factor was race and the confounding factor was hospital the ratio of hospital (row) totals is (59% / 28% = 2.1) which exceeds the ratio of race (column) totals (64% / 47% = 1.4) leading to the possibility of reversal in conclusion. [article on Cornfield's condition].)

Jan 22/09. We added to: Bradford Hill Criteria of Causation: Many apparent associations later turn out to be false. When does a study show causation between a risk factor or treatment and the disease? Even if an association is established between a risk factor and a disease it does not necessarily follow that the risk factor caused the disease. Maybe a third factor caused both or perhaps early forms of the disease result in the so-called risk factor so that causation works in the opposite direction. For example:
  1. Third Factor. In a Jan 2009 paper, researchers found that prostate cancer patients had more frequent sexual activity when young than non-prostate cancer patients. The authors did not conclude that sexual activity in youth causes prostate cancer, despite the association. In particular, they did not conclude that modifying one's sexual activity would modify the risk for prostate cancer. Rather, they hypothesized that there was a third factor, hormone levels, that caused both. [news item] [PMID: 19016689 If their hypothesis were correct this would be an example of association without one of the associated factors causing the other (because a third caused both).
  2. Reverse Causality. Fat people are the ones that drink diet coke (association) but that does not mean that diet coke makes people fat (causation).

Jan 16/10. We added to Bradford Hill Criteria of Causation: Simpson's Paradox. In investigating possibly discriminatory behavior in prostate cancer treatment it was found that at University Hospital that: (1) nearly the same percentage of white men and black men were offered prostate cancer surgery (59% white, 58% black). (2) At VA Hospital the percentages were also the same (28% white, 28% black). Yet overall 50% of white men were offered prostate cancer surgery and only 32% of black men. How is it possible that black men were offered surgery less often in total even though they were offered it just as often as white men at each hospital. The actual numbers from the study were:
University Hospital54/91 (59%)7/12 (58%)61/103 (59%)
VA Hospital11/40 (28%)22/79 (28%)33/119 (28%)
Overall65/131 (50%)29/91 (32%)
The reason for the discrepancy between the overall results and the results in each hospital is that most blacks went to the hospital that is less likely to use surgery (regardless of whether you are black or white) and not because they were less likely to be offered sugery in the same circumstance as a white. Looking at it the other way, if we had originally been told that 50% of whites were offered surgery vs. 32% of blacks we might have thought that the doctors provided a different treatment to blacks and whites. Its only when the confounding factor of hospital is brought into play that the data shows that this is not the case. We thought we were comparing treatment across races but because race was associated with hospital and hospital had a larger effect than race we were actually comparing hospitals more than race. It was only after we corrected for hospital by looking at the results at each hospital separately that this became apparent. Its only when the confounding factor of hospital is brought into play that the data shows that this is not the case. We should always be aware that an unknown confounding factor may reverse apparently clear associations. JCO 2007 v25 2117-2121.
This can appear in various forms. A study is comparing two treatments but the apparently worse treatment could actually be the better treatment had it been tested on sicker patients. Upon comparing the success rates of two surgeons it might be that the one with the lower success rate is actually the better surgeon if he is given the harder to treat cases.

Jan 13/10. In Can Most Studies be Wrong we add: For those who wish to read about meta analyses in depth see the book Michael Borenstein et al, Introduction to Meta-Analysis, 2009. It has 400+ pages and has all the formulas but is written in a very easy to read style so that if you skip them you will still come away with a significant understanding.

Jan 10/10. Added to Free Monthly Prostate Cancer Magazines and Journals: An August 2009 paper [PMC 272388] [PMID: 19672442] lists the [top cited 100 papers in urology]. the [rankings of countries of origin of the top 100 papers], [rankings of institutions of origin of the top 100 papers] and the
[most common authors among the top 100 papers]

Jan 10/10. In Advice to the Newly Diagnosed we added: Paraphrasing Paul Kienow, the resolution to Whitmore's conundrum is that for low risk cancers just about any treatment option has a high cure rate whereas none do for high risk cancers.

Jan 5/10. The following reference to placebos was added to Bradford Hill Criteria of Causation: [Placebos].

Jan 5/10. In RP vs. LRP vs. RLRP - Part 1. Open Surgery (RP) we added: A November 2009 survey of about 80 open surgeons found that (1) caseloads of open surgery were declining due to a shift to robotic surgery and (2) the existence of robotic surgery has influenced open surgeons "to modify their surgical technique, reduce convalescence, and alter follow-up recommendations". This includes reducing the incision length, steps to reduce operative time, steps to reduce blood loss and transfusion rate, adoption of new instruments, modification of the dissection technique, increasing use of hemostatic agents and other measures. [PMID: 19630483].

Jan 3/10. In Lycopene, Selenium and Vitamin E in Combination we added: Fleshner et al who performed the research below themselves announced negative results on the benefit of E combined with selenium and soy. [news release] at the 2009 AUA Annual meeting.

Jan 1/10. In How Healthy Men Can Reduce Their Risk we added: A 2008 paper by Walz et al also found Free PSA to have prognostic value at lower PSA levels as well. [PMID: 18853417]. A calculator based on this paper intended only for situations where PSA is less than 2.5 inputs the DRE status (normal or suspicious) and Free PSA value and outputs the probability that a biopsy will find cancer.

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