If you decide that you are going to study a group of people just one time, in a single session, that research design is called cross-sectional research. An obvious pro, or advantage, to cross-sectional research is that it is relatively easy and inexpensive. It's also easier to do your study using a large group of people because you only need them for a single session. It's easier to get people to agree to be in a study if it only takes a single hour or single day. However, a con, or disadvantage, to cross-sectional research is that you cannot study whether people change over time. That's where the second type of research comes into play.