Types of Research Designs in Psychology

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  • 0:49 Descriptive Studies
  • 1:16 Case Studies
  • 2:03 Correlational Studies
  • 4:38 Experimental Research
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Lesson Transcript
Instructor: Ellie Green

Ellie holds a B.A. with Honors in English from Stanford University. She is pursuing a Ph.D. in English Literature at Princeton University.

What are the three main research designs, and what are their advantages and disadvantages? In this lesson, you'll explore the different goals behind descriptive, correlational and experimental research designs.

Psychological studies begin as questions. 'How does a person with severe brain damage behave?' 'Do smart parents have smart children?' 'How does reminding someone of their race or gender change their performance on a test?'


Psychologists turn these questions into hypotheses: 'Do smart parents have smart children?' is changed to 'Parents who have high scores on intelligence tests have children with similarly high scores.' Then they design a study to test the hypothesis in an efficient way that reduces potential confounds, or factors that could explain the results but aren't directly measured or addressed by the study. Depending on the question, and on the hypothesis, psychologists will choose one of three main types of research designs.

Descriptive Studies

A first type of research design is called descriptive. Descriptive studies aim only to gather data to present a complete picture of a given subject. Psychologists might use a survey to assess the state of mental health on college campuses. The results wouldn't tell them anything about the causes of mental illness in college students, but it would give a complete picture of the problem. To answer one of the questions we began with, 'How does a person with severe brain damage behave?' psychologists might use a case study, or a close examination of one person with a particular problem. Phineas Gage, a railroad construction foreman in the nineteenth century, is a classic example of such a case study: in an accident at a railroad construction site, he had a large metal rod driven through his head. He not only survived but was fully-functioning and lived for another twelve years. But several people close to him remarked that they noticed his personality had changed, that he'd become irritable and unable to hold a job. Though Gage's case alone could not prove anything definitive about his particular brain injury and emotion regulation, it did help psychologists make better hypotheses about the relationship between these things for future studies. Descriptive studies often form the basis for later correlational or experimental research.

Correlational Studies

Correlational studies try to figure out the relationship between two or more variables, which could be anything you can measure like behavior, age, gender, etc. To answer the question, 'Do smart parents have smart children,' two variables psychologists might measure are parents' IQ and children's IQ. Psychologists would then administer IQ tests to a very large number of families and determine statistically how related the parents' scores were to the children's scores--this 'relatedness' is known as the 'correlation.' A correlation is represented by a number called the Pearson correlation coefficient that is between -1 to 1. If two variables have a correlation of 0, there is no relation between them--for example, something like your birthday and the color of your hair would likely have a correlation very close to 0 because these two things have nothing to do with each other. A correlation between 0 and 1 is called positive, and it means that as the first variable increases, so does the second one. This turns out to be true in the case of parent and child IQ; one study reports a moderately positive correlation of .35. A correlation between -1 and 0 indicates a negative correlation, and means that as the first variable increases, the second decreases. Age and memory function are likely to be negatively correlated; as age increases, the ability to remember things clearly tends to decrease.

Correlation is not causation; for example, high parental IQ does not necessarily cause a high child IQ
Causation Illustration

An important shortcoming of correlational research is the problem of determining causation. As tempting as it might be to assume so, correlation is not causation. Though there is a moderate positive correlation between parents' IQ and children's IQ, this does not mean that a high parental IQ causes a high child's IQ. Though in this particular case it seems unlikely that the parents' high IQ's are caused by the child's, this is a possibility that cannot be ruled out by correlational research. It is also possible, even likely, that both high IQ's are caused by a third external factor, like high income and socioeconomic status.

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