CREATED 3/21/2010
USAWARNING:
This site deals only with the corporate corruption of science, and makes no inference about the motives or activities of individuals involved.
There are many reasons why individuals become embroiled in corporate corruption activities - from political zealotry to over-enthusiastic activism; from gullibility to greed.
Please read the OVERVIEW carefully, and make up your own mind.
|
OPINION ONLY
retrospective/prospective studies
Epidemiology has both prospective (forward looking) and retrospective (backward looking) studies.
In a retrospective study the disease has already been identified in the subject, and the investigator tries to ascertain the connection between some possible causative agent and the occurrence of the disease.
He/she investigates the connection between the history of exposure to the causative agents and people who have the disease, and then compares them to the exposure of a matched group of subjects who do not have the disease — comparing the relative frequencies of exposure to the possible causative agent.
In a prospective study the investigator assembles a cohort (a matched, group of similar people) who do not have the disease (as far as can be ascertained). He/she then ascertains from each of the individuals in that cohort their exposure to whatever agents or combinations of agents the investigator is investigating.
That cohort of people is then followed up for months or years to measure the rate of occurrence of disease (or death from disease) in which there is the interest.
This is then compared to the frequency of the exposure to that causative agent in those who subsequently are found to have the disease (or die from it) and those that do not.
Epidemiology in the 1950s
Prospective studies were favoured in the 1950s because investigators felt that it was important to establish unequivocally that the direction of the association was: first the exposure to the tobacco smoke, and then the subsequent occurrence of the disease.
But these prospective studies are also subject to certain limitations.
1. You won't have any useful results from your study for many years ... and in the case of slow-acting chronic diseases, it may be many decades. In the meantime, people suffer.
2. You can have problems with selection bias in prospective studies. Conceivably, this could be the addition of individuals into the cohort you plan to study, on some basis that would selectively discriminate for or against the exposure to that agent.
In the retrospective study , you ascertain the association of the agent (say smoking) and the occurrence of the disease at the same time; whereas, in a prospective study, you very clearly establish the exposure to the agent before there has been any knowledgeable occurrence of the disease.
[Also] in a prospective study, you can have access to a more general population, even a representative sample of the total population. So it's accessed to a wider population ... a more typical, more representative population than is usually the case with a retrospective study where, typically, the limitation is to people who are hospitalized.
They may be different in many respects, of course. One is that they have a disease from the general population.
[Source: 1996 Nov 4 Deposition of Lester B Breslow for Mississippi vs Tobacco litigation.  
]
Smoking Prospective studies - the first was Doll with British Doctors. The American and Canadian veteranrs, another Californian men [100454221] `
|
WORTH READING
|
