Psychology 101: Intro to Psychology

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.

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 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.

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.

To determine causation, psychologists must conduct experimental research. This also involves variables, but in this case they are distinguished as independent and dependent. Psychologists change the independent variable and look at what happens to the dependent variable. Some psychologists hypothesized that women and racial minorities might experience something called stereotype threat when they take tests. Since these groups are stereotyped as not being as good at math as white men, the anxiety they experience by worrying that their performance will confirm this negative stereotype actually makes them end up doing worse. Psychologists have tested this in many situations, using awareness of race or gender identity as the independent variable and test performance as the dependent variable. One group administered a difficult section of a standardized test to two groups of African-American and European-American students. The first group was led to believe that the test measured intelligence; the second was not. In the first group, there was a wide performance gap between African-American and European-American students; in the second group, this gap was greatly reduced. The researchers concluded that worrying about confirming negative stereotypes about intelligence had actually made the African-American students perform worse. Similar results have been found for women in chess competitions and entrepreneurship.

Experimental research is powerful but limited in an important way: psychologists simply can't manipulate all the variables they're interested in. Sometimes it's just impossible. If psychologists are interested in the differences between female and male leadership, they can't just instate a female leader in a company formerly led by a man; the company board might have something to say about that. Sometimes experimental research is possible but highly unethical; to experimentally determine what kinds of trauma were most likely to cause post-traumatic stress disorder, for example, psychologists would have to submit large numbers of people to different kinds of trauma and potentially debilitate them with PTSD symptoms for the rest of their lives.

Let's quickly go over the three types of research designs once again. Descriptive studies seek only to document; a case study like Phineas Gage is an example of this. Correlational studies try to establish a relationship between two variables, like parents' IQ and children's IQ, though correlation does not equal causation. Finally, experimental research looks to study causation, like with the example of stereotype threat and test performance, but can't be used in every situation due to practical and ethical concerns.