1. Introduction to Case Study Control

Understanding and determining of epidemiology and the distinct cause of disease is very important. There are two methods of studying the same- cohort study and case-control study. Case control study is a type of observational or ecological study which takes into consideration the comparison of certain attributes. Such epidemiological observational studies are used in the field of medicine. It is frequently compared with cohort studies which will be discussed further. As it is an epidemiological study, it increases the ‘how frequent or whys’ of study. The analysis of case control study depends on various testing factors like relative risk, probability and also the assumptions for the occurrence of the disease.

The control factors vary according to the well-being of an individual- for the sick person and for a person with good health and so, an accurate observation is to be made and this forms the basis of observational study by comparing various factors in the form of case-control study. This observational study includes the retrospective cohort and cohort study. These types of studies are mainly applicable or used in medicine and are related to the epidemiological study.


a) Advantages of Case Study Control

  • Case-control studies are carried out by small terms and by individual researchers.
  • They are designed in such a manner that they are always progressive and in a stage of advancement.
  • Case-control study is less expensive and thereby more cost efficient as compared to that of the cohort studies.
  • They have greater statistical value and hence provide much more precise and accurate results for the observations made therein.
  • It is a less time-consuming process.
  • They are effective for rare diseases having long latency reaction or response period towards exposure of disease.


b) Disadvantage of Case Study Control

  • Case-control studies may not always be successful as they have their own limitations. They do not provide more evidence when compared to other observational studies and hence the chances of confusion of various factors can arise leading to the extension of associated risk factors of the disease.
  • When the risk factor arises, there occurs a problem to extend the timeline for the exposure of disease and the outcomes are erroneous.
  • One of the major drawbacks is that this study is more difficult to obtain the reliable and appropriate information about individual’s health issues and conditions which keep changing from time to time. Hence, this study is somewhat underrated where precision and accuracy of evidence or observations are required.
  • They are used only in selection basis.
  • They prove to be ineffective in rare exposures where control parameters cannot be effectively designed.


c) Example of Case Study Control

One of the most significant examples for the case-control study is the observation of link between smoking and the lung cancer. This study was done by Richard Doll and Bradford Hill. The study was made in a forum and discussions were made between the forum members. The debating members arrived at the conclusion that this type of study may not accurately reveal and prove the results that smoking is the cause of about 87% mortality deaths of lung cancer in US.

To prove this, two groups were made- the exposed subjects and the controls. The results were initially analyzed and then tested with the exposed subjects among the reported cases and with the controls for areas such as risk factors, probabilities and the disease assumption. Later, it was proven that disease assumption is not important and ratio of exposure can be directly used to estimate the ratio of results. Hence, this analysis proves to be a good Case control study example.


Fig.1-Methodology of case control study

2. Cohort Study

Cohort study is a type of medical research used in the analysis of the cause of disease and to establish the links between risk factors and health outcomes. Cohort Studies are also known as “prospective” studies i.e., they are planned in advance and carried out in future for a specific period of time. Generally speaking, this study is projected towards future. That is to say, that cohort studies are forward-looking.

In this type of study, researchers investigate on a research question and then find a hypothesis about the causes of the disease. Then, they observe a group of people for over a certain period of time, collect data and detect the changes that take place within them. Cohort studies are used by epidemiologists looking into the factors that affect individual health and illness. Some of the terms that relate to cohort studies may be said to be- incidence, longitudinal, historic and forward-looking. This study finds the cause and roots of the particular disease and hence is proven to be more advantageous.

a) Features of Cohort Study

  • Cohort studies observe large groups of individuals and record their changes in coherence to the exposure of possible cause of the disease.
  • Cohort studies are considered to be better than case-control study.
  • They are regarded as the most well- designed form of medical research and are proven to be better for the observational purpose.

b) Disadvantage of Cohort Study

  • Prospective case control study is not suitable for rare diseases.
  • They are more expensive and generally take many years and sometimes even decades before the results can be provided.
  • They can only provide clues about the causes for the disease, and this might differ from the actual situation in certain cases.

c) Example of Cohort Study

One of the famous examples for the cohort study can be attributed to the Nurses’ health study that was undertaken to analyze the women’s health. It was a massive, long-run analysis of women’s health that was originally started in 1976 and this study focused on the second generation cohort of nurses in 1989 and the third generation cohort of nurses from US and Canada in 2010. Numerous insights into health were made by the researchers and it was run by the Harvard School of Health.

Another popular example for cohort study is associated with the study analysis that was made by UK researches in 1958. The study concentrated on the 17,000 people which were all born in the same week in different regions of Britain. And, the centre for longitudinal studies launched studies with new large groups of babies. Recently, the latest study is the millennium cohort study, focusing on 19,000 millennium babies and children born in UK in 2000-2001. This study focuses on the general health and behavioral patterns of these children.

Cohort studies are good at finding relationships between health and environmental factors such as chemicals in air, water and food. WHO (World Health Organization) helps to coordinate with the separation of cohort studies and results as a whole. These results and large amount of data are used for analysis of cancer.


Fig.2-Analysis of Nurses’ health study

3. Retrospective Cohort Study

Retrospective Cohort Study is also known as Historic Cohort Study. In this type of study, a group of individuals share a common factor to which they had been exposed in order to determine the influence on the development of disease, which is then compared with the other group of individuals who had not been exposed to it. It is also known as Longitudinal Cohort Study. Longitudinal cohort study is a field associated with medical and psychological research where the records of group of individuals who look alike but differ by a certain characteristic are compared for a certain outcome. In this type of study, the researcher collects the data from past records and does not observe the patients for a long period of time as the main aim is to establish the current disease status or position in both the exposed and the unexposed groups. Preventive measures have to be taken as errors may arise due to the risk factors and health assumptions.


a) Advantages of Retrospective Cohort Study

  • They require less time to compete and are better while analysing multiple outcomes.
  • They can be effectively used for rare diseases to a great extent.
  • Retrospective cohort study proves to be less expensive than case control study.


b) Disadvantages of Retrospective Cohort Study

  • Some factors or statistics cannot be measured.
  • They are based on selection basis in order to study the effect of only a few factors.
  • Accurate comparisons cannot be made between the exposed and unexposed group of individuals, since there might be other environmental factors affecting the actual results due to longer time durations before the results are obtained.

c) Example of Retrospective Cohort Study

This example is based on the study of the employees of a tyre manufacturing company. Initially, the past records of the employees are collected and the data is not interpreted for a long time. Meanwhile, there are chances that the apprehensions may not be in proper coherence when results are obtained. The study only reveals the comparison how the employees are affected by the exposure to the chemicals and the effect of group of individuals who are not exposed.


Fig.3-Interpretation of longitudinal study

4. Comparisons

Case Control Study V/s Cohort Study

Case Control Study

          Cohort Study

1. We study about disease and analyze if we can associate risk factors to it.

2. It is done for rare diseases.

3. This process is for a small period of time.

4. This study is more expensive.

5. This is similar to an observational study.

1. We study about risk factor and analyze if we can associate a disease with it.

2. It cannot be done for rare diseases.

3. The study can last for decades and years.

4. Cohort study is less expensive.

5. This study is forward-looking.

Case Control Study V/s Retrospective Cohort Study

Case Control Study

Retrospective Cohort Study

1. This study is based on selection basis.

2. Case study is an observational study based on factors like odd ratio, disease assumption.

3. Case study concentrates on frequent analysis of cases and control

1. This study is based on selection basis.

2. This study is based on medical and psychological research.

3. Retrospective study compares two groups of individual under exposure and those not under exposure.




Fig.4-Comparisons of case study, cohort and retrospective study

5. Future Aspects

Various types of studies related to the medicine and epidemiological research have been discussed and their comparisons have been studied. Still, there are various advancements to be done in this field for the betterment and improvement of people’s health medically.