Critique a retrospective cohort study

Even if it was clear who was exposed to tire manufacturing chemicals based on employee records, it would also be important to take into account or adjust for other differences that could have influenced mortality, i. For example, it might be important to know whether the subjects smoked, or drank, or what kind of diet they ate.

retrospective cohort study statistical analysis

You then determine the proportion of cases who were exposed to any risk factor of interest in the past, and compare this with the proportion exposed in the control group.

Key Concept: The distinguishing feature of a retrospective cohort study is that the investigators conceive the study and begin identifying and enrolling subjects after outcomes have already occurred.

Retrospective descriptive study

However the same scientific principles as would be expected in the original studies need to be applied to the identification, sorting and analysis of potentially relevant studies. Verbatim quotes of participants can be used to illustrate these themes. Some Study Designs….. They then determine whether the subject subsequently developed the outcome of interest. Suppose investigators wanted to test the hypothesis that working with the chemicals involved in tire manufacturing increases the risk of death. The study is generally retrospective because it looks backwards in time to the earlier exposures of individuals. Ideally, assignment of subjects to one of the comparison groups should be done randomly in order to produce equal distributions of potentially confounding factors. The groups being compared differ in their exposure status. You then determine the proportion of cases who were exposed to any risk factor of interest in the past, and compare this with the proportion exposed in the control group.

Disadvantages[ edit ] Retrospective studies have disadvantages vis-a-vis prospective studies: Some key statistics cannot be measured, and significant biases may affect the selection of controls. They can classify them as "exposed" or "unexposed" based on their employment records, and they can use a number of sources to determine subsequent outcome status, such as death e.

Retrospective studies pros and cons

Design[ edit ] The retrospective cohort study compares groups of individuals who are alike in many ways but differ by a certain characteristic for example, female nurses who smoke and ones who do not smoke in terms of a particular outcome such as lung cancer. You then determine the proportion of cases who were exposed to any risk factor of interest in the past, and compare this with the proportion exposed in the control group. Retrospective cohort studies require particular caution because errors due to confounding and bias are more common than in prospective studies. For more on this topic see the module on Intervention Studies. The Nurses Health Study Home Page Pitfall: Note that in these prospective cohort studies a comparison of incidence between the groups can only take place after enough time has elapsed so that some subjects developed the outcomes of interest. It can take many forms including in-depth interviews and focus-groups with analysis attempting to identify underlying themes. Retrospective Cohort Studies In contrast, retrospective studies are conceived after some people have already developed the outcomes of interest. Retrospective cohort studies like the one described above are very efficient for studying rare or unusual exposures, but there are many potential problems here. RCTs are by definition prospective. Each arm of the study is then followed up and the amount or severity of the disease measured in the intervention group and compared with the control group. At the end of the period of observation the incidence of disease or frequency of health outcome in the exposed group is compared to that in the unexposed group. The most obvious sign that a review is systematic will be the presence of a methods section. However the same scientific principles as would be expected in the original studies need to be applied to the identification, sorting and analysis of potentially relevant studies. The analysis always occurs after a certain number of events have taken place.

Controls without the health outcome are then chosen. RCTs are by definition prospective.

Retrospective cohort study pros and cons

Their design is very similar to that of a prospective cohort study. A case-control study belongs to the observational group of studies. Since the data analysis occurs after some outcomes have occurred, some students mistakenly would call this a retrospective study, but this is incorrect. A qualitative study examines the experiences and beliefs of people from their own perspective. What is a Systematic Review? Suppose investigators wanted to test the hypothesis that working with the chemicals involved in tire manufacturing increases the risk of death. Irrespective, both groups are then followed, often over long periods of time. Date last modified: July 19, Sometimes exposure status is not clear when it is necessary to go back in time and use whatever data is available, especially because the data being used was not designed to answer a health question. Participants individuals or groups are randomly allocated to receive either the new intervention being tested or a control treatment usually the standard treatment or a placebo. It begins by choosing individuals who have a health outcome or disease whose cause you want to investigate. Each arm of the study is then followed up and the amount or severity of the disease measured in the intervention group and compared with the control group. RCTs are by definition prospective.

Frequently there will have been more than one study addressing a particular health question.

Rated 7/10 based on 77 review
Download
Prospective and Retrospective Cohort Studies