What is a cross-sectional study
A cross-sectional study makes inferences about a population at one point of time. The purpose of these studies is not to follow up with the audience but to collect the data once. When the investigator repeats the cross-sectional study with later surveys he does not choose the same sample rather he takes another sample. The investigator can ask questions from the whole population of interest or if it is too large he can take a subset of that population.
Data collection in cross-sectional studies
The investigator can use any method of data collection like a questionnaire, interview or observation method. For example, an elementary school teacher assumes that having protein rich diet in breakfast help children be more active in the school. She can send questionnaire to her students’ parents to fill them and give her back to know what they eat in the breakfast and to compare it with the children activity and participation in the school. This will help her conclude whether her hypothesis is true or false. The survey done in cross-sectional study is usually simple and no baseline data is collected no follow up is needed. The questions are usually simple and no control over the extraneous factors can be maintained by the investigator.
Difference between cross-sectional and longitudinal studies
In cross-sectional studies the investigator collects the data at one time and he can use any method of data collection that is best suitable. This study will not be as generalizable as other studies might be. The investigator can use an appropriate sampling method and can collect data from the whole population of interest if it is convenient or he can draw sample. On the other hand, in longitudinal studies the investigator collects data once and than repeat the same survey again from the same population and can do the same several times over a duration of time. The purpose of longitudinal studies is to compare the results and analyze the change that has happened over a period of time.
These studies can be conducted on routine bases in social sciences, medical sciences and in economics. In comparison to other type of studies they do not take much time and can give results. These studies give meaningful information for a group of people and hypothesis testing can be done on a small scale in small time frame.
The main disadvantage is that it does not yield as generalizable data as many other type of studies. These studies provide a snapshot of a single point in time and do not provide before-and-after results or data. We cannot say for sure that the results are truly representative and one cannot establish the cause and effect relationship.