The longitudinal study uses time as the main variable, and tries to make an in depth study of how a small sample changes and fluctuates over time.
A cross sectional study, on the other hand, takes a snapshot of a population at a certain time, allowing conclusions about phenomena across a wide population to be drawn.
An example of a cross-sectional study would be a medical study looking at the prevalence of breast cancer in a population. The researcher can look at a wide range of ages, ethnicities and social backgrounds. If a significant number of women from a certain social background are found to have the disease, then the researcher can investigate further.
This is a relatively easy way to perform a preliminary experiment, allowing the researcher to focus on certain population groups and understand the wider picture.
Of course, researchers often use both methods, using a cross section to take the snapshot and isolate potential areas of interest, and then conducting a longitudinal study to find the reason behind the trend.
This is called panel data, or time series cross-sectional data, but is generally a complicated and expensive type of research, notoriously difficult to analyze.
Such programs are rare, but can give excellent data, allowing a long-term picture of phenomena to be ascertained.
This means you're free to copy, share and adapt any parts (or all) of the text in the article, as long as you give appropriate credit and provide a link/reference to this page.
That is it. You don't need our permission to copy the article; just include a link/reference back to this page. You can use it freely (with some kind of link), and we're also okay with people reprinting in publications like books, blogs, newsletters, course-material, papers, wikipedia and presentations (with clear attribution).