The aim behind retrospective study design is to study some event, phenomenon or situation that has been happened previously. There are only two ways to collect data for a retrospective study: either the investigator collect information from written evidences like from books, magazines, newspapers, diaries and other personal records, or he asks the respondents who can recall the situation. Asking the respondents about the situation is only possible if the event was happened in a certain time period in the past if the event happened several decades or years back the investigator cannot get the data from people rather he has to rely on written records.
Problems with retrospective study design
Retrospective studies have several chances of bias because first hand information is not possible in this case. The investigator relies on second hand information or secondary sources of information. The authenticity of second hand information cannot be made sure completely. However, these studies cannot be conducted using any other study design therefore, the investigator is left with the only option to use the retrospective study design. The investigator needs to take special caution to avoid the chances of bias in the retrospective study designs. The investigator needs to take large sample size to avoid the chances of bias. He should also maintain that he has made the right selection of the evidences to get information about the past event that he is studying.
Advantages of retrospectives studies
The advantages of retrospective studies include the time saving nature of these studies as well as the benefit that they can be conducted on a small scale. The baseline as well as the outcomes have already happened before the study is conducted therefore the investigator can study multiple problems at the same time. It is very helpful in studying medical situations that happened in the past. It is also helpful in studying medical conditions that are rare and have little or no evidences in the present situation to study.
Examples of retrospective study designs
- To study the impact of Mughal dynasty on the subsequent Muslim civilizations of Indo-Pak.
- To study the impact of World War II on the living conditions of France today.
- A historical analysis of the inventions during the Victorian Era in the Europe.
- A historical analysis of the type of employment preferences among the people of California from 1990-2017.
- An analysis of the types of crimes committed in the northern region of USA from 2000-2010.
These and other type of descriptive studies come under the retrospective study design. The similarity among these studies is that the investigator cannot do experiments to collect first hand evidence rather he has to collect data from secondary sources. The results of these studies can be helpful in determining the future trends in the same situation but they cannot be generalized to any similar future event.