Home > November - Volume 24 - Issue 11 > Case Control Studies: Design, Conduct, Analysis. PDF Only. Case Control Studies: Design, Conduct, Analysis. Schlesselman Book Reviews: PDF Only . COPD and Occupational Exposures: A Case-Control Study. The case-control approach is as old as clinical medicine itself, but in a quantitative sense the method is of recent vintage. Perhaps for this reason, case- cont.
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Case-Control Studies: Design, Conduct, Analysis (Monographs in Epidemiology and Biostatistics) [James J. Schlesselman] on tisidelaso.gq *FREE* shipping. Trove: Find and get Australian resources. Books, images, historic newspapers, maps, archives and more. control studies. ▫ Understand key considerations in designing a case-control study A case-control study is usually conducted before a cohort.
In the denominator, we find the proportion of woman-years on the pill divided by the proportion of woman-years of non-use. Among the control subjects, the ratio of exposed to unexposed is expected to be the same as the ratio of the woman-years—except for sampling fluctuations. We still obtain, on average, the same rate ratio of 4.
It follows that to estimate the rate ratio, we do not have to measure, nor to estimate, all the person-years of pill-using and non-using women in town; we can simply determine the ratio of those woman-years by asking a representative sample of women free of CHD from the population from which the cases arise, about their pill use.
The great advantage of case—control studies is that we can calculate relative incidences of disease in a population, by collecting all the data for the numerator by collecting cases in hospitals or registries where they naturally come together , and sampling control subjects from the denominator, i.
Thus, one achieves the same result as in a comprehensive population follow-up, at much less expense of time and money. Just imagine the effort of having to do a follow-up study of all women of reproductive age in town, also keeping track of when they move in and out of town and constantly updating their oral contraceptive use in a particular calendar year!
Advanced teaching Cohorts vs dynamic populations For researchers who are used to think in terms of clinical cohorts, it can be difficult to understand that populations are not depleted: is it not true that the people with a particular risk factor will develop some disease more often, and thus in the course of time, there will be less of them who are still candidates for developing the disease?
That will be true in cohorts because their membership is fixed, but not in dynamic populations.
One way to understand this is to think of genetic exposures. People with blood group O develop clotting disorders more frequently, whereas people with blood group A develop more often gastric cancer.
However, in a dynamic population, the numbers of people with blood group O or A are not constantly depleted—blood group distribution is fairly constant over time, as new people are born with these blood groups so that an equilibrium is maintained.
For the aforementioned discussion, we assumed that we were studying all women living in a town during some time over the course of one calendar year this could be the whole year or a few months. The situation would be entirely different if we restricted our study to all women who lived in the town on the 1 January of that year: then we would only count the myocardial infarctions that happened during this year in women who had been living in town on the 1 January; indeed, the number of women on the pill might decline more than the number of women not on the pill because the myocardial infarctions predominantly occur in the users.
That situation would be akin to a clinical cohort study, i.
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By and large, as with blood groups, the population denominator remains constant in terms of its exposure distributions: the woman-years of oral contraceptive use vs non-use.
To refine the concept, the members of a dynamic population do not necessarily have to be present for long periods in the population—as might be surmised from the examples about towns and countries of which one is either an inhabitant or not, and usually for several years.
Members of a dynamic population may also switch continuously between being in and out of the population. The risk periods of interest are the periods when people drive.
The exposure of interest is phone use. In a case—control study, car accidents are sampled, and it is ascertained say, via mobile phone operators whether the driver was phoning at the time of the accident.
Control moments might be sampled from the same driver say, in the previous week or from other drivers, by sampling other moments of time when they were driving; for each of these control moments, it might be ascertained, via the same mechanism as for the cases, whether they were phoning while driving. These control moments are contrasted with the moment of the accident the case. But what if the exposure distribution in the population is not in steady state?
That situation is depicted in Figure 2. The bold undulating lines show the increasing use of one type of oral contraceptives and the decreasing use of the other type during the time period risk period. The finer lines below it depict individuals who enter and leave the populations of users of these types of oral contraceptives.
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Case-Control Studies: Design, Conduct, Analysis
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Schlesselman Pages: Oxford University Press Language: English ISBN Description this book Please continue to the next pageCase-Control Studies:However, it is important to note that a positive relationship between exposure and disease does not imply causality.
Advanced Search. Advantages and disadvantages Compared to other types of studies, the case-control variety can provide significant results in a relatively short period of time, and requiring little resources ,.
Design and data analysis case-controlled study in clinical research
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