Very often, in understanding many social phenomena such as poverty or in studying developmental trends across the lift span, the method of longitudinal study is commonly used as a research design to examine the same group of targets repeatedly over an extended period of time. In this article, we shall discuss this popular research methodology in the area of social sciences.
What is a Longitudinal Study?
A longitudinal study is a correlational research that involves the same sample of research participants or subjects to be examined or observed repeatedly over long periods of time, often many decades,
typically to investigate problems of developmental psychology or to uncover predictors of certain diseases in medicine.
In the medical field, for instance, most longitudinal studies examine associations between exposures to known or suspected causes of disease and the corresponding
mortality arose from that disease. To do this the researchers have to identify a sample of subjects exposed to a risk factor along a sample of unexposed controls, compare their incidence rates and finally estimate the attributable and relative risks. Two common types of a longitudinal study are cohort study and panel study.
Cohort Study
A cohort study is a method of research by tracking one (or more) cohort(s), defined as a group of people with a time-specific common experience such as being born or getting married in the same year, over a period of time to examine how exposures affect their outcomes. This method of research was first developed by demographers and applied primarily to the study of fertility.
One of the advantages in conducting a cohort study is that subjects need not be assigned on a strict random basis. In addition, the method can be used with either raw or administrative data and is highly flexible in providing insights into the effects of a mix of different factors regarding social, cultural and political change.
On the other hand, it may sometimes be difficult to examine the causal nature between a suspected risk and the outcomes in a cohort study which are subject to the influence of other factors beyond control such as cultural, political or social impacts. These aspects may affect or even be contradictory to the outcomes and lower the validity of the study results. Moreover, the long time span required by a cohort study would inevitably invite challenging changes over the course of study and again pose new threats to the validity of the study results.
Panel Study
A panel study follows the same sample of people at an extended period of time, either on a regular or need basis, with a view to monitoring developmental or other changes, or predicting long-term or cumulative effects. Unlike a cohort study, the research participants or subjects need not have any time-specific common experience.
The merits of conducting a panel study are that it can reveal both net and gross changes in the dependent variable, as well as shifting attitudes and patterns of behavior. Also, as competing stimuli are allowed to appear and influence on the subject, the study results could reveal dynamics of change that might go unnoticed with other research approaches.
However, the above merits of a panel study would diminish if adequate number of sample units cannot be recruited or secured during the study period. Also, in order to derive valid cause-effect
relationships, three necessary conditions must be maintained.
i) the cause must precedes the effect;
ii) there is a covariation between the cause and effect variables; and
iii) all alternative explanations must be ruled out.
Application
The use of longitudinal study has a long history in many countries. For example, the longitudinal study of the Office of Population Censuses and Surveys prospectively followed a 1% sample of
the British population that was initially identified at the 1971 Census to relate outcomes such as mortality and incidence of cancer to employment status, housing, and other variables measured at successive censuses.
In Minnesota, the Institute of Child Development of the University of Minnesota conducted a longitudinal study of parents and children since 1975 on 267 first-time mothers and their children to trace the course of individual development and to understand factors such as children’s temperament, parent-child interactions, adaptation in early adulthood, balance between work and family roles, etc. that guide it toward good outcomes or poor outcomes. The study is currently in its 31st year.
In the early 80’s, a longitudinal study was conducted in the US under the support of the National Broadcasting Company to investigate whether there is a causal influence between violent TV viewing and aggression among young people. Information on aggression, TV viewing and a host of sociological variables from a panel of 1 200 boys were collected six times for the three year study period.
The Australian Government is currently funding a longitudinal study of Australian children under its Stronger Families and Communities Strategy to examine the impact of its unique social and cultural environment on next generations. In addition to enriching the understanding of early childhood development and providing more information for social policy debate, the results would be used to identify opportunities for early intervention and prevention strategies regarding children development.
More examples on longitudinal study can also be observed in many other countries like Germany, Singapore and Japan on other social phenomena. With this research method, scientists and
researchers are able to develop more theories to understand the case-effect relationship in their areas of study.
References:
(1) Panel study [http://www.socialresearchmethods.net/tutorial/Cho2/panel.html]
(2) Longitudinal study [http://www.encyclopedia.com/doc/1O87-longitudinalstudy.html]
(3) Cohort study [http://www.encyclopedia.com/doc/1O88-cohort.html]
[http://www.socialresearchmethods.net/tutorial/Cho2/cohort.html]
(4) Minnesota [http://cehd.umn.edu/icd/Parent-Child/PCPOverview.html]
