Cross-Sectional vs. Longitudinal Design
The first decision a researcher must make is whether to test a group of people at a single moment in time or whether to test a group of people several times, across many days, weeks or even years. Imagine you need to make this decision. What are the pros and cons of each choice?
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.
If you decide that you want to study a certain group of people over multiple sessions, or over an extended period of time, that research design is called longitudinal research. You can remember the name 'longitudinal' because it starts with the word 'long,' meaning a long period of time. The advantages and disadvantages of longitudinal research are the exact opposite of cross-sectional research. With longitudinal research, you can follow people over time, which means that you can see how their thoughts or behaviors change across different locations, when they are around different people or simply as they age.
For example, imagine you are studying happiness. You could study whether someone who is happy today is still happy next week, next month and next year. In this way, you might gain insight into the stability of emotions by using longitudinal research. However, the disadvantage of longitudinal research is that it is more expensive and time consuming, and often it's difficult to get volunteers for the study due to their increased time commitment.
Types of Studies
The difference between cross-sectional and longitudinal research applies to every particular type of study. Next, we need to cover different types of studies. Again, each choice has advantages and disadvantages.
Imagine that you want to study happiness in children. This example will be used for the rest of the lesson to illustrate the differences between each type of research design.
The first option you have is called a case study. A case study is defined as the use of a single person in a research study. For our example of studying happiness in children, imagine that a particular child has been identified by his teachers as always being extremely happy. A researcher might study this child in-depth to attempt to understand why he is so happy.
The advantage of a case study is that it allows a researcher to gain a lot of in-depth, detailed information due to the close examination of this single case. However, a disadvantage is that what you learn about this particular person might not be true of anyone else. So, it may be difficult to make general conclusions about what makes other people happy because you only really know about this single person.
The next option researchers have is called a field study, or sometimes this is called a naturalistic study. Here, instead of asking participants to come to a strange lab to be studied, the experimenters observe the participants in their natural environments.
For example, if you wanted to study happiness in children, you might observe children at school or on a playground. Don't get confused and think that just because it's called a 'field' study, you actually have to go out into a field! The term simply means that you are not in a lab. Instead, you are in a natural environment.
The advantage of a field study is that the behaviors you observe will certainly be more natural because, ideally, you are simply watching what would have happened anyway, even if you weren't there. The disadvantage of a field study is that you have no control over the environment, so you can't really test the impact of changes to that environment, and you can't really ask the participants any questions because that would be interrupting their natural behaviors.
Perhaps the most common type of research in psychology is a survey study. This is exactly what it sounds like. Researchers give a group of people a survey with lots of questions, and the participants simply answer the questions. For example, a researcher could ask every child in a certain school to fill out a questionnaire about what makes them happy or unhappy.
The clear advantage to this type of study is that it is easy, simple and inexpensive, and a researcher can get hundreds of people to complete the survey in a relatively short period of time. However, there are some disadvantages to survey studies. One disadvantage is that it's difficult to truly test the impact of certain variables when all people are doing is filling out a survey. Another disadvantage is that some people might not be honest in their survey responses.
The classic type of research is the true experiment, which is when a researcher creates two or more groups of people to compare. In a true experiment, the difference between the groups is something under the control of the experimenter. When each person is assigned one group or the other, that assignment is random. Therefore, this aspect of experiments is called random assignment.
For example, let's say that you have a hypothesis that children who get healthy lunches in school are happier than children who get unhealthy lunches. You could control the lunches of two different classes by randomly deciding which class gets which kind of lunch. Then, compare the happiness level of each group. If the two groups are identical in every way except the lunches and they do experience different levels of happiness, you can say that it was due to the difference in lunches.
You'll learn more about experiments in another lesson. But for now, just know that the main advantage of experiments is that you have control over the situation, so you can make hypotheses about cause and effect within the environment. The main disadvantage is that experiments require a lot of advance planning and control over the participants for them to be done correctly.
The final type of research design is a quasi-experiment. You just learned about true experiments, where researchers compare two or more groups that they have created. In contrast, in a quasi-experiment, researchers are still comparing two or more groups, but the groups were not created by the experimenter. Instead, they occurred naturally. In other words, quasi-experiments do not have random assignment.
For example, let's say that you wanted to compare the happiness levels of boys versus girls. Here, you would be comparing the two groups, but you did not create the groups. You did not select a participant and randomly assign them to be a boy or girl. That choice was made much before you came around.
Another example might be that you want to compare older children to younger children, in terms of their happiness. Again, you could compare several different age groups, but you didn't create the groups; they happened naturally. Quasi-experiments compare across groups that occur naturally and were not created by the experimenter.
The advantage of quasi-experiments is that they often answer interesting questions, such as gender or age differences. But, the disadvantage is that we can't really be sure of why any differences occur. For example, let's say that we do find that boys are happier than girls. We still don't know why that difference exists. It might be something biological, or it might be how boys are raised differently than girls, or it might be that girls are not given as many social advantages as boys. Until we do a true experiment where we can sort out these different possible causes, a quasi-experiment is helpful in identifying differences across naturally occurring groups but not in telling us why those differences exist.
In summary, many different types of research are possible. Longitudinal research studies people over an extended period of time, whereas cross-sectional research studies people only in a single session. A case study is when we examine a single person, to get in-depth information. Field studies occur in natural environments, such as school or work settings. Survey studies allow researchers to gain a lot of information quickly, from a lot of people. Experiments let researchers compare two or more groups of people they have created by manipulating something in the environment. Quasi-experiments let researchers compare two or more naturally occurring groups, such as boys vs. girls or teenagers vs. adults. Any of these types of research can allow psychologists to answer questions about how and why people think and behave.
After watching this lesson, you should be able to define cross-sectional research, longitudinal research, case studies, field studies, survey studies, experiments and quasi-experiments, and understand the advantages and disadvantages of each.