What is a Retrospective Study?
Retrospective, the term comprises two words i.e. “retro” which means “in the past” and “spective” which means “to look”. Thus, a retrospective analyzes the events of information that had already occurred in the past. In a retrospective study, the outcome of the reference studies has already occurred before a retrospective study is initiated. The researcher or an author of a retrospective study can collect the data from the registry. In a retrospective study, after the collection of data, the research question is framed. An example of a retrospective study is to compare the occurrence of lung cancer in people who smoke and who do not smoke.
What are the Advantages of Retrospective Study?
Retrospective studies have the following advantages:
Less time consuming and cheaper: Retrospective studies are cheaper and require less time for completion. As the data related to the study is already available and the researcher compiles and compares the data between and subjects and control, retrospective studies provide immediate results.
Effective in rare disease: Retrospective study is quiet effective in rare diseases. Data related to the rare disease is available from various centres to arrive at an evaluable study population. This allows for greater accuracy of study results.
Initial screening: Sometimes the retrospective studies are done as an initial screening for prospective studies. As prospective studies are time-consuming and costlier, the hypothesis to be tested through prospective studies can initially be tested through retrospective studies.
No-follow-up: Retrospective studies uses the data already available in the literature or the registry. Thus, there is no risk of loss of follow-up in retrospective studies.
Large data-set: Retrospective makes use of large data-set. This may provide more accurate results.
What are the Types of Retrospective Studies?
There are mainly three types of retrospective studies. These are:
Retrospective cohort studies: This study is also known as the historic cohort study. This study is done to analyze the effect of a factor on the occurrence of the disease. These studies may help to analyze multiple outcomes.
Case series and case reports: Case reports are a type of retrospective study in which the researcher reports symptoms or instructive case that was not previously seen with a medical condition. Case reports are a group of multiple unusual case series.
Case-Control Studies: Case-control studies are better than case series and case reports. This is because there is a control arm in these studies which provides an effective comparison.
What is a Prospective Study?
Prospective studies are done in the present to analyze the outcome in the future. In the prospective study, the information is required to be generated and is not available before the start of the study. An example of a prospective study is to follow-up with a group of alcohol drinkers to identify whether drinking alcohol for 10-years is linked to liver disease. It is to be noted that none of the subjects enrolled under the study should have the outcome of interest. For instance, in the above example, none of the subjects should have liver disease before the start of the study. The follow-up is an important and inherent property of prospective study and loss of follow-up may affect the outcome of the study.
What are the Advantages of Prospective Study?
Following are the various advantages of prospective study:
New disease risk factors: Prospective studies are important in analyzing the risk factors for new diseases for which the data is not available. This will help in the effective management of the disease.
Accurate results: Because of well-controlled study design and accurate generation of data, the results provided by prospective studies are relatively more authentic.
Detailed data analysis: Detailed analysis of the outcome and other statistical factors can be done in prospective studies. Exposure can be measured before the outcome and the incidence and disease process can also be determined.
Multiple outcomes: Multiple outcomes can also be obtained from prospective studies.
No risk of recall bias: As the prospective study does not require any data recollection from the past, the risk of recall bias is eliminated.
What are the Various Types of Prospective Studies?
There are generally three types of prospective studies:
Prospective trend studies: In this study, the samples are taken from the dynamic population in which the individuals change over time.
Prospective panel studies: In such studies, the measurement is done on the same set of individuals.
Prospective cohort studies: In the prospective cohort studies, the measurement is done on the individuals from the same pool of individuals.
What is the Difference between Retrospective and Prospective Study?
Following are the differences in prospective and retrospective studies:
Data: In the prospective study the data is generated by the researcher after enrollment of the subjects while retrospective studies make use of the already available information.
Control: Prospective study has more control over the subjects and data generation as compared to retrospective studies.
Accuracy: More accurate results are provided by prospective studies due to less biasness and optimum data control.
Time and cost: Prospective studies are more time-consuming and costlier as compared to retrospective studies.
Biasness: The risk of recall biasness is eliminated in prospective studies.
Practicality: Prospective studies are both observational and interventional while retrospective studies are only observational.
Usefulness: Prospective studies are useful in cases of emerging new exposures while retrospective studies are not of much use in such scenarios.