Cohort studies can be carried out in two different ways: you can arrange the cohorts together and accompany them in future (prospective cohort study), or you can access data from the past so that you can analyze the present (retrospective cohort study). In order to be able to implement one of these types of cohort analyses, the following steps need to be taken:
- Define the research question and aim: to obtain relevant information, you have to ask the right questions. Only when you have concrete ideas about the content and purpose of the investigation, can you create the necessary structure of the study.
- Define cohort events: the second step is to define the events in which cohorts occur, as these can lead to an answer to the research question.
- Determine relevant cohorts: now you determine which and how many cohorts are to be parts of the study. It is also possible to split or specify the formed cohorts.
- Perform the cohort study and evaluate it: if the desired cohorts have been found, you can carry out the respective type of study (prospective/retrospective, inter/intra cohort study) and interpret the data received.
The changes in behavior you want to obtain by carrying out the cohort analysis are determined by three factors or effects. The evaluation and weighting of these are the main tasks of interpretation:
- Cohort effects
- Age effects
- Period effects
Cohort effects are the behavioral differences and changes between different cohorts. They can be generally explained by the existence of different social and environmental influences. Age effects, on the other hand, are the changes that can be attributed to the increasing age of people and their related attitudes. Lastly, period effects represent behavior changes that result from changing environmental conditions – regardless of generational and socio-demographic factors.
From these three effects, you can notice any clear trends regarding the behavior of individual groups. On the basis of these trends, you can use them to develop future prognoses or solution strategies. The main task is to separate age, cohort, and period effects, which can occur in every result, from each other. If you include these as identification problems in the cohort analysis, you can find a clear reason for the behavioral changes.