The goal of a retrospective study is to investigate a previously occurring event, occurrence, or circumstance. A retrospective study can only collect data in one of two ways: the investigator obtains data from written material such as books, magazines, newspapers, diaries, and other personal documents, or he asks respondents who can recollect the situation. Inquiring into the issue with the responders is only practicable if the event occurred within a specific time period in the past; if the event occurred several decades or years ago, the investigator will have to rely on written documents.

Design flaws in retrospective studies
Because first-hand knowledge is not possible in retrospective studies, there is a risk of bias. Secondhand information or secondary sources of information are used by the investigator. It is impossible to guarantee the accuracy of second-hand information. These research, however, cannot be undertaken using any other research project design, leaving the investigator with just the retrospective study design as an alternative. In retrospective study designs, the investigator must exercise extreme caution to avoid the possibility of bias. To eliminate the possibility of bias, the investigator must use a large sample size. He must also assert that he has chosen the appropriate evidence to obtain information about the historical event he is researching.

Retrospective studies have a number of advantages.
The time-saving aspect of retrospective studies, as well as the fact that they can be undertaken on a small scale, are also advantages. Because the baseline and outcomes have already occurred prior to the investigation, the investigator can focus on numerous issues at the same time. It's particularly useful for researching past medical issues. It's especially useful for researching medical laboratory project topics conditions that are uncommon and have little or no evidence to study right now.

Retrospective study designs examples

To investigate the impact of the Mughal dynasty on Indo-following Pak's Muslim civilizations.
To investigate the effects of World War II on France's current living conditions.
A historical examination of inventions in Europe during the Victorian era.
From 1990 to 2017, a historical review of the types of jobs that people in California preferred.
From 2000 to 2010, an examination of the types of crimes perpetrated in the northern United States.

The retrospective study design encompasses these and other forms of descriptive investigations. The investigator in these investigations has to acquire data from secondary sources because he cannot conduct experiments to collect first-hand evidence. These studies' findings may be useful in predicting future trends in the same situation, but they cannot be applied to any other future occurrence.