An investigation into a previously occurring event, occurrence, or scenario is known as a retrospective study. Only written sources, such as books, journals, newspapers, diaries, and other personal documents, or persons who recall the scenario, can be used in project topics retrospective examination. If the incident occurred within a specified time frame, the investigator can only interrogate the responders; if the incident occurred decades or years ago, the investigator will have to rely on written documents.

Retrospective studies with design errors
There is a potential of bias in retrospective studies since first-hand information is not possible. The investigator uses secondary sources of information or secondhand knowledge. The accuracy of secondhand information is impossible to guarantee. However, no other study design can be used in these trials, leaving the investigator with only the retrospective study design as an option. In retrospective study designs, the investigator must exercise considerable caution to avoid bias. The investigator must employ a large sample size to eliminate the likelihood of bias. He must also state that he has chosen appropriate evidence in order to comprehend the historical event he is researching.

There are several advantages to retrospective investigations.
Retrospective investigations are advantageous since they save time and allow for small-scale implementation. The investigator can focus on numerous issues at the same time because the baseline and outcomes have already occurred previous to the investigation. It's quite handy for locating information about previous medical issues. It's especially valuable for examining unusual medical disorders where there's little or no evidence to study right now.

Examples of retrospective study designs
To look into the impact of the Mughal dynasty on Muslim cultures in Indo-Pakistan
Examine the effects of World War II on France's current living standards.
A look back at the inventions that took place in Europe during the Victorian era.
A look back at the types of employment that people in California favored from 1990 to 2017
An analysis of the types of crimes committed in the northern United States from 2000 to 2010.

These and other types of descriptive inquiry are included in the retrospective study design. Because he cannot perform experiments to acquire first-hand evidence in these situations, the investigator must rely on secondary sources for data. The outcomes of these education research topics may be valuable in anticipating future trends in the same environment, but they cannot be applied to any other circumstance in the future.