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Medical Forum / Diseases and Disorders / Cancer / March 2005Misuse of statistics in medical research
I have prepared an article on the misuse of statistics in medical research. If the subject is of interest to you or if you work with cancer, you might be interested to read it. Your opinion would be appreciated. To read the article, click here: http://www.geocities.com/benny_patrick/stats.html Fabrikant >I have prepared an article on the misuse of statistics in medical > research. If the subject is of interest to you or if you work with [quoted text clipped - 5 lines] > > Fabrikant Some of your complaints, such as the misuse of relative risk and the quite small benefits from certain medical interventions are valid. But this does not look right to me --- "Now let us see, how the study results deal with the pitfalls mentioned in the previous section. We do not have to deal here with stability of the basic data, because on the page 784 of the publication [3] it is mentioned that at three years of study, 81% of patients in perindopril group were actually taking the medication. This means, that 19% of the perindopril group did not take the medication and de-facto belonged to the placebo group. The number of patients in perindopril group has to be re-calculated as n2=6110*0.81=4950 and the difference of 1160 patients added to the placebo group, so that n1=6108+1150=7268. The percentages are computed as p1=603/7268=8.3% and p2=488/4950=9.9%. Now the placebo group is safer than the perindopril group and their difference p1-p2= -1.6%, according to formula (1), is statistically significant with the confidence interval greater than 99.7%. Does this prove that perindopril is dangerous for the health? Of course, not, but it does prove, just how shaky is the basis, on which the authors of the study made their conclusions. " Those patients not taking the drug at three years would presumably have taken the drug for a while, and it destroys the whole point of randomisation to later transfer them to the placebo group. It CANNOT be done. It is proper to include them in the "treated" arm, even if doing so actually has the effect of diluting any benefits from taking the drug. Dilutes the benefits? Yes. You are deceptively including them in the placebo group without knowing, or allowing for, what their primary outcomes were. If these patients showed the same morbidity as the rest of the placebo arm then the figure of 603 in the above calculation is quite wrong - it should be increased by (9.9% of 1160) = 116), making a mockery of your calculations. Peter Moran. . >>I have prepared an article on the misuse of statistics in medical >> research. If the subject is of interest to you or if you work with [quoted text clipped - 41 lines] > > Peter Moran. . BTW You are also wrong about breast cancer. In every advanced country the mortality rate is distinctly decreasing even as the incidence continues to rise. You can confirm with the national statistical agencies of England America, and Australia. Peter Moran >>>I have prepared an article on the misuse of statistics in medical >>> research. If the subject is of interest to you or if you work with [quoted text clipped - 48 lines] > > Peter Moran Although this is largely a stage migration effect, Peter..... >>>>I have prepared an article on the misuse of statistics in medical >>>> research. If the subject is of interest to you or if you work with [quoted text clipped - 51 lines] > > Although this is largely a stage migration effect, Peter..... No it's not. These are absolute mortality figures. These are the number of people per hundred thousand of population who end up with "breast cancer" as the cause of death on their death certificates. You are thinking of survival rates, which will be affected by overall earlier diagnosis and other factors. Peter Moran >>>>>I have prepared an article on the misuse of statistics in medical >>>>> research. If the subject is of interest to you or if you work with [quoted text clipped - 60 lines] > > Peter Moran No, if the proportion of early stage cancers diagnosed goes up (as it has due to mammography and other screening), absolute mortality goes down. Stage for stage, the 5, 10 and 15 year survival for breast cancer is only marginally better than it was 20 years ago, if at all > "Peter Moran" <moringa@gil.com.au> wrote in message >>>> BTW You are also wrong about breast cancer. In every advanced country >>>> the mortality rate is distinctly decreasing even as the incidence [quoted text clipped - 13 lines] >> >> Peter Moran > No, if the proportion of early stage cancers diagnosed goes up (as it has > due to mammography and other screening), absolute mortality goes down. Yes. That is usually called earlier diagnosis, and it is one probable factor in the declining mortality . Stage migration is usually used to refer to spurious stage-specific benefits, when there is no true reduction in either overall or individual mortality. > Stage for stage, the 5, 10 and 15 year survival for breast cancer is only > marginally better than it was 20 years ago, if at all Then where is the declining mortality coming from? There must be fairly significant improvements in survival rates in early stage breast cancer to produce the figures shown in the graph at http://www.statistics.gov.uk/cci/nugget.asp?id=575. Stated there: "Death rates gradually increased up to the mid 1980s and then began to fall around the time that screening started. By 1998 mortality was around 20 per cent lower than it would have been (based on predictions of pre-screening rates in various age groups)." The widening disparity between incidence and mortality of breast cancer could have many contributing factors: earlier diagnosis, better treatment, changes in breast cancer biology, and even a small contribution from overdiagnosis in marginal pathology, but there is no disputing the declining death rates. Peter Moran >> "Peter Moran" <moringa@gil.com.au> wrote in message > [quoted text clipped - 44 lines] > > Peter Moran But the biggest factor is that the proportion of early (and VERY early) cancers compared to the total is now much higher than 20 years ago. More early cancers in the group = better overall mortality in the group. That's a stage-migration effect in this colony, at least......... > But the biggest factor is that the proportion of early (and VERY early) > cancers compared to the total is now much higher than 20 years ago. > More early cancers in the group = better overall mortality in the group. > That's a stage-migration effect in this colony, at least......... Your dispute with Moran would benefit, if both of you operate with facts and numbers, rather than having a discussion of the kind "is not!" - "is so!" I have looked at the ACS data from 1930 to 1990. The mortality practically did not change during 60 years, variating between 25 to 28 per 100,000 of population, and this variation looks quite random, clearly independent from the level of mammography and/or any medication. Seekers of success though found a reason to celebrate: they claim that the increase of number of diagnosed cases, which did not result in increased mortality is a 20% success. How about a simple explanation that the increased diagnostics is due to increase in false positive? Nobody knows, how many perfectly healthy women lost their breasts for nothing and live under illusion that they survived breast cancer? What is the probability that the early diagnosis and treatment would save almost exactly the number of lives, which would leave the total mortality almost unchanged? Fabrikant >> But the biggest factor is that the proportion of early (and VERY early) >> cancers compared to the total is now much higher than 20 years ago. [quoted text clipped - 20 lines] > > Fabrikant False positives may be an issue with mammograms. But much less with biopsy path, and there are approximately 0 false positives with the final formal meastectomy/lumpectomy pathology. Or are you suggesting that there are lots of women who have surgery for benign lesions, and are never told? If so, you are psychotic > False positives may be an issue with mammograms. > But much less with biopsy path, and there are approximately 0 false > positives with the final formal meastectomy/lumpectomy pathology. > Or are you suggesting that there are lots of women who have surgery for > benign lesions, and are never told? > If so, you are psychotic I am not psychotic; read the news. We hear now and then, women suing their doctors for cutting off their breast for no good reason. I remember one such show on Dateline. Now, does one need much brain to understand that this is a tip of the iceberg? Ok, what is your explanation that diagnostics increased by about 20% and at the same time mortality decreased in such a proportion that mortality per 100,000 remains practically unchanged for the past 60 years? Just a coincidence? Why don't you address the rest of my comments? Fabrikant >> False positives may be an issue with mammograms. >> But much less with biopsy path, and there are approximately 0 false [quoted text clipped - 7 lines] > remember one such show on Dateline. Now, does one need much brain to > understand that this is a tip of the iceberg? An open mind is not the same as an empty mind. You have read too many conspiracy theories. How many cases of "women suing their doctors for cutting off their breast for no good reason" can you list? If you can list any, how many of them were found to have merit? I didn't think so. > Ok, what is your explanation that diagnostics increased by about 20% > and at the same time mortality decreased in such a proportion that > mortality per 100,000 remains practically unchanged for the past 60 > years? Just a coincidence? Many oncologists will agree that the stage specific survival for breast cancer has not changed much in 40 years, but the non-stage specific survival certainly has, almost certainly because of screening, and the fact that a much larger proportion of BC is now stage 1 than it was 20 years ago. Does that mean that treatment is responsible for the improvement? No. But it's an improvement, none the less. > Why don't you address the rest of my comments? Because I'm having difficulty getting you to see the facts even in this one. > Fabrikant > Then where is the declining mortality coming from? There must be fairly > significant improvements in survival rates in early stage breast cancer to [quoted text clipped - 13 lines] > > Peter Moran Please, read my article attentively: I do discuss the argument that the transfer of some patients from medicated group to placebo group involves possible transfer of the number of outcomes. My point is not uniquely based on this transfer, but rather on instability of data, where a +/-5% of change in the initial data changes the conclusion. I also show that 2% difference between groups can be easily explained by reasons, other than the study medication. So, I suggest that you take the article as a whole and address all the argumentation. About success being diluted. I remind you the main proposition of null-hypothesis: you have to presume the medication to be USELESS, unless proven otherwise. So, you can not presume, that those, who do not take medication are in worse situation that those, who do. Fabrikant |
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