From the Reference Guide to Epidemiology of the Federal Judicial Center’s Reference Manual on Scientific Evidence, the principal reference for instructing US courts in regard to epidemiology. The Manual states: “…epidemiology cannot objectively prove causation; rather, causation is a judgment for epidemiologists and others interpreting the epidemiological data.” , and “.. the existence of some [associated] factors does not ensure that a causal relationship exists. Drawing causal inferences after finding an association and considering these factors requires judgment and searching analysis.”  and “[w]hile the drawing of causal inferences is informed by scientific expertise, it is not a determination that is made by using scientific methodology.”.
Thus, while epidemiologists insist that their discipline is a science, clearly it is not the solid experimental science that produces reliable causal connections to fuel new scientific discoveries, successful technological advances, and defensible public health policies. More to the point, if multifactorial epidemiology does not operate in the framework of science, what warrants of reliability could it offer?
It remains a fact that in over 50 years of trying to induce cancer in animals using tobacco smoke, not even one study has yielded a statistically significant result that links cancer to tobacco use
Although there is substantial evidence of the health benefits of moderate drinking, there has been a continued campaign on the part of many alcohol opponents to suppress or deny these findings. For instance, Harvard epidemiologist Carl Seltzer, a co-investigator on the Framingham study, found positive effects of moderate drinking on heart disease 25 years ago. Seltzer was denied permission to publish these results by the US National Heart and Lung Institute on the grounds that an article about such results would be “scientifically misleading and socially undesirable in view of the major problem of alcoholism that already exists in the country.” (C. Seltzer, Journal of Clinical Epidemiology 1997 50: 627-629, “Conflicts of Interest” and “political science”)
Arnott once again raises the myth that smokers die prematurely; this is easily refuted.Allow me to give you an example of why these studies show misleading results
Suppose that you were to compare the mortality of people who did their main grocery shop at a discount store, to the mortality of people who shopped at an expensive/high-end grocery store, You would most likely find that the people who shopped at the discount store died younger than those who shopped at the up-market store. You might (erroneously) conclude that it was the products being consumed that affected mortality, when in reality the two groups are not directly comparable, as people who shop at up-market stores tend to be wealthier and live longer anyway .
This scenario explains why for example, cigar smokers appear to live longer than non-smokers. The reason being that cigar smokers are over represented in the most affluent echelons of society.
Professor Peter Finch , when analysing Australian smoking mortality, found a difference in life expectancy of only a few days. this might be explained by the fact that Australia is a society that has a less noticeable differential between rich and poor.
If you wish to find out something about a particular population , and it is not feasible to test the whole population, then you may test a sample of that population providing that the sample is an accurate refection of the population. In order to get a valid sample one needs to select randomly across the the entire population.
Something to be avoided is self-selection.; this is in fact the major flaw in virtually all drug trials, in that they ask for volunteers, and this leads to bias.
You might be thinking What's wrong with using volunteers?
Well, consider the following: Suppose you wished to ascertain the feeling of the general public towards the recent Olympic games. You might perhaps create a web-site asking people to complete a survey about the games. The flaw in the sample is here quite easy to spot. Only those who were interested in the games would volunteer, and therefore your sample would not reflect the the general population, some of whom must not be interested in the games.
This sampling problem is of course due to having to obtain consent from the subject when dealing with human-beings, you can't force people to take part.. Although the US government have done precisely that in the past. Chemical and biological weapons were used on civilian populations without their consent in the following locations:
Watertown, NY and US Virgin Islands (1950)
SF Bay Area (1950, 1957-67)
St. Louis (1953)
Washington, DC Area (1953, 1967)
Savannah GA/Avon Park, FL (1956-58)
New York City (1956, 1966)
One type of study that does not suffer from this flaw is a mortality study. So for instance you might wish to find out if LDL cholesterol increases mortality .from heart disease Here you can simple select a period , say a year, and then record the age of death and the LDL cholesterol level of the deceased,
In fact a major study along these lines was conducted along these lines:
In an eight-year study of about 26,000 men and women in Isehara, Kanagawa Prefecture, the death rate of men whose LDL cholesterol levels were between 100 mg/dl and 160 mg/dl was low, while the rate rose for those with LDL cholesterol levels of less than 100 mg/dl.
The LDL figures exhibited less influence on women, but the death rate still rose for women with LDL cholesterol levels less than 120 mg/dl.
A separate study of 16,850 patients nationwide who suffered cerebral stroke showed the death rate of people with hyperlipemia who died from a cerebral stroke was lower, and their symptoms more slight.
It is a complete myth that smokers die prematurely
smoking rarely kills male ever-smokers before 50 years of age and female ever-smokers before 55 years of age, and does so very rarely at earlier ages. While deaths attributed to smoking do occur much more frequently with increasing age, so too do deaths from other causes and it is not clear how the ever-smoker's age-increasing annual risk of death due to his or her smoking should be apportioned between smoking on the one hand and simply aging on the other. The anti-smoking movement's message that smoking kills has to be interpreted from the balanced perspective of not only how likely it is to do so; but of how likely it is that other causes will pre-empt that possibility by leading to death before it eventuates. For instance, while it may be a cause of concern to a 65 to 69 year old male ever-smoker, and to a 70 to 74 year old female ever-smoker to be told that they have a yearly chance of about 1 in 100 that their smoking will kill them,that particular concern will not, perhaps, seem quite so overwhelming when they learn that, in any event, they also have about a 1 in 50 chance that they will die from other causes. To put the extreme case, an 80 plus year old ever-smoker is unlikely to be overly concerned that he or she has about a 1 in 30 yearly chance that it is their smoking that will kill them, when the yearly chance that other causes will do so is about 1 in 10.
extract from The Smoking Epidemic: Death and Sickness among Australian Smokers
Prof.Peter D. Finch
I live in a small university town. I often chat with under-graduates and am constantly surprised to find that my old O-level grasp of their subject is usually as good as, if not better than, theirs. Why is that, when educational standards have never been higher?