Five Basic Types of Research Studies | Organization for Autism Research

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There are five basic types of research studies, each designed to answer different kinds of questions. The five types of studies are discussed below. 

1. Case Studies

Case studies look at a single subject (e.g., a child with autism) or a single case (e.g., a classroom for children with autism). Case studies are typically used in research that describes the development of an individual, group, or situation over a period of time in order to provide a detailed account of what is occurring within its real-life context.

  • The advantage of a case study is that it allows the researcher to gather a lot of information about one person or one case.
  • The disadvantage of a case study is that the information gathered about one person or a small group of people cannot readily be applied or generalized to other people or other cases in other situations or other settings and, therefore, may be of limited use.

Click here to check out a sample case study. 

2. Correlational Studies

Correlational studies look for a relationship between two or more variables, or things, that naturally occur in the same environment. Correlational studies cannot tell us anything about cause and effect, only that there is a relationship between two or more things. For example, a study might be designed to determine if there is a relationship between the number of children with autism in a particular community and the month of their birth.

Figure 1 presents a bar graph of a study of number of children with autism and month of birth. The graph illustrates that more children with autism were born in the winter months (November, December, and January) than in the summer, spring, or fall.

Although this graph shows a relationship between cases of autism in one community and month of birth, we cannot make the assumption that a winter birthday causes autism. Perhaps some other variable that we have not considered (such as an illness) is having an effect on the two variables under study.

  • The advantage of correlational studies is that a lot of information about a large number of people can be gathered at one point in time.
  • The disadvantage of correlational studies is that it is not possible to control other factors outside of the study that might influence the research.

Click here to check out a sample correlational study.

3. Longitudinal Studies

Longitudinal studies can give us information about how people develop over time. These types of studies follow one group of people (referred to as a cohort) across time, measuring the same behavior multiple times. For example, we may want to determine if children with autism do better on performance tests in self-contained than in inclusive classrooms. The best research design for answering this question would be to follow one cohort of children with autism that spent time in both environments.

In Figure 2, this design is presented with a line graph.

As illustrated in the graph, children in this cohort performed better in grades 1 and 4 when they were in inclusive classrooms than in grades 2 and 3 when they were in self-contained environments.

  • The advantage of longitudinal studies is that they allow researchers to pinpoint times during development when changes occur.
  • The disadvantage of longitudinal studies is that it takes a long time to complete them. (Note that in the example in Figure 2, the study took four years to complete.)

Click here to check out a sample longitudinal study.

4. Experimental Studies

Experimental studies are controlled so that the researcher manipulates one variable to determine its effect on other variables. Two primary types of experimental studies are used in intervention development and testing: randomized group design and single-case design.

The first type includes experimental group designs in which participants are randomly assigned either to receive the intervention (the experimental group) or to a control group. The control group completes all the same steps as the experimental group, except they do not receive the intervention that is under investigation. Therefore, if the study is well controlled, it can be concluded that the differences between the experimental and control groups at the end of the study are due to the intervention.

A second type of experimental study frequently used in intervention research is single-case design (SCD). Many studies involving children with autism, particularly those examining behavioral and educational treatments, use single-case designs. Rather than examining differences across participant groups that do and do not receive an intervention, single-case designs involve individual participants or a small cluster of participants who provide their own control for comparison. For example, a researcher may be interested in determining whether a new communication intervention tool on tablet devices improves communication skills.

  • The advantage of randomized experimental studies is that the research design allows researchers to examine cause-and-effect relationships.
  • The disadvantage of a randomized experimental study is that the results cannot always be generalized to the real world. This is because this kind of study lacks “real-world” authenticity; that is, what occurs in a controlled environment of a study may be very different from what might occur in a real-life setting, such as a typical classroom.

Click here to check out a sample experimental study. 

5. Clinical Trial Studies

Clinical trial studies are one specific type of randomized group experimental study. Clinical trial studies are most likely to be conducted in medical or other clinical settings. Similar to experimental group design studies, clinical trial studies employ an experimental/control group, in which participants are randomly assigned to receive the experimental treatment (e.g., a medication to treat autism symptoms) or a placebo (a sugar pill).

In both randomized experimental group and clinical trial studies, participants are not informed about their group assignment to guard against participant expectations about intervention or treatment. In addition, in well-designed studies, experimenters are not informed about group assignment either to guard against researcher expectations about intervention or treatment. That is, if participants expect to get better because they know they are receiving treatment, they may actually get better; similarly, if researchers expect an intervention to be successful, they may perceive it as so, regardless of whether or not the treatment is actually effective! This uninformed state is what researchers refer to as being blind to the conditions of the experiment. When both participants and experimenters are uninformed, it is referred to as a double-blind study, and is a means of ensuring objective results.

  • The advantage of clinical trial studies is that they can determine the effectiveness of an intervention. This is because the intervention is compared with a placebo or control condition.
  • The disadvantage of clinical trial studies is the same as for randomized experimental studies; that is, the results of the study cannot always be generalized to a real-life setting.

Click here to check out a sample clinical trials study.

Reading and interpreting research can be a difficult task. However, with perseverance and practice, you can learn to comfortably navigate scientific writing for the purposes of making informed treatment decisions for your child. This section is written to give you a basic understanding of the scientific model underlying research studies. Check out OAR’s A Parent’s Guide for Research for more information.


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