A researcher who is about to conduct a study on a specific field usually has research objectives and questions. Based on these, the researcher chooses a research design that will be most appropriate for the study. A cohort study is a research design where the researcher studies a group of people, also known as a cohort, for a longer period of time. On the other hand, a case-control study is a research design used by researchers where the research begins with an outcome to comprehend the cause.
All Modules Cohort Studies and Case-Control Studies The cohort study design identifies a people exposed to a particular factor and a comparison group that was not exposed to that factor and measures and compares the incidence of disease in the two groups.
A higher incidence of disease in the exposed group suggests an association between that factor and the disease outcome. This study design is generally a good choice when dealing with an outbreak in a relatively small, well-defined source population, particularly if the disease being studied was fairly frequent.
The case-control design uses a different sampling strategy in which the investigators identify a group of individuals who had developed the disease the cases and a comparison of individuals who did not have the disease of interest.
The cases and controls are then compared with respect to the frequency of one or more past exposures. If the cases have a substantially higher odds of exposure to a particular factor compared to the control subjects, it suggests an association.
This strategy is a better choice when the source population is large and ill-defined, and it is particularly useful when the disease outcome was uncommon. Examples of two real outbreaks will be used to illustrate these differences in sampling strategy. Health officials noted that an unusually large number of cases had been reported during a span of several days.
The table below summarizes some of the salient facts about Salmonella infections. Descriptive epidemiology was conducted, and hypothesis-generating interviews indicated that all of the disease people had attended a parent-teacher luncheon at a local school.
In fact, it was a potluck luncheon, and the attendees each brought a dish that they had either prepared at home or purchased. The descriptive epidemiology convincingly indicated that the outbreak originated at the luncheon, but which specific dish was responsible?
The investigators needed to establish which dish was responsible in order to clearly establish the source and to ensure that appropriate control measures were undertaken. Diarrhea, fever, abdominal cramps, vomiting. Paratyphi produce typhoid with insidious onset characterized by fever, headache, constipation, malaise, chills, myalgia; diarrhea is uncommon and vomiting is usually not severe.
Contaminated eggs, poultry, unpasteurized milk or juice, cheese, contaminated raw fruits and vegetables alfalfa sprouts, melons. Typhi epidemics are often related to fecal contamination of water supplies or street vended food.
Other sources include pet rodents hamsters, mice, and rats, or their bedding and reptiles and amphibians e. Of these, 45 attendees agreed to complete a questionnaire regarding the foods that they had eaten at the luncheon.
Since they had a relatively small, discrete cohort and a fairly high incidence of disease, a cohort design was a logical choice. For each dish served at the luncheon the investigators compared the incidence of Salmonellosis between those who ate a particular dish the exposed group and those who had not eaten that dish the non-exposed comparison group.
For each dish they constructed a contingency table to summarize the result from the survey. For example, the table below summarizes the findings from the survey regarding the incidence of disease in those who ate the cheese appetizer compared to those who did not eat it.by Annette Gerritsen, Ph.D.
Two designs commonly used in epidemiology are the cohort and case-control studies. Both study causal relationships between a risk .
Stroke risk factors in an incident population in urban and rural Tanzania: a prospective, community-based, case-control study. A case-cohort study is similar to a nested case-control study in that the cases and non-cases are within a parent cohort; cases and non-cases are identified at time t 1, after baseline.
In a case-cohort study, the cohort members were assessed for risk factros at any time prior to t 1.
by Annette Gerritsen, Ph.D. Two designs commonly used in epidemiology are the cohort and case-control studies. Both study causal relationships between a risk factor and a disease.
Cohort and case-controls studies 1. COHORT VS. CASE-CONTROL STUDIESAdriana Pérez Fortis Case control studies trace backwards from outcome to exposure. Cohort studies: Study Case-control studies: groups are defined by Study groups are defined exposure.
by outcome. Case-control studies Advantages Disadvantages Is the most efficient. In case-control, one starts from the outcomes i.e. cases and bases/controls/referents (matched or not), and tries to study what the exposure was.