The influence of an intervention, occurrence, circumstance, or therapy over time is studied using longitudinal research methods. The investigator investigates the population once and records it, then continues to collect data from the same respondents over time to determine the influence of time on the impact of an intervention or circumstance. For both government and commercial enterprises, this is a highly effective form of research design. These groups gather data throughout time to determine how and when the impact began, as well as how it altered. It may also be used to investigate a community's health state.

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Examples
From 2010 to 2017, research the immigration patterns of IT-related Indian people to the United States.
To investigate the infertility patterns in a community over a period of time.

The purpose of this study is to look at the prevalence of breast cancer in northern American women over a period of time.

To conduct a survey of a certain neighborhood about firsthand evidence of crime over a specific time period.

The goal of this study was to look at domestic violence in California suburbs from 2005 to 2017.
Longitudinal research has a number of advantages.
Longitudinal studies are extremely useful for government organizations collecting data on the population in various areas of life. The health department, for example, collects data to learn about changes in the prevalence of a disease following the implementation of a therapy. Unlike before-and-after investigations, the goal of this sort of study is to determine the pattern of change rather than just the level of change. These studies are also carried out by commercial firms in order to improve the quality of their product or service. They ask people questions throughout time and gather data on a regular basis. These investigations have advantages that are not available in other sorts of research.

Disadvantages

The downsides of the longitudinal research design include that because they are long studies, respondents may lose interest in participating. Respondents may answer survey questions casually and without consideration; nevertheless, respondents should be made aware of the seriousness of the survey and its significance so that they are completely responsible for their responses. When a study takes a long time, some respondents may not want to participate and may drop out after a few sessions, which can be a difficult situation for the investigator.