There are several different types of research methods, many of which can be combined in a single research project. These include:
 

Longitudinal research - where the same individuals are studied over a long period of time. Terman's study of gifted children (discussed in your textbook)is probably the most famous example of this.
 

Cross-sectional research - where different individuals are studied at the same time.

Your textbook discusses the advantages and disadvantages of each of these types of designs. A major advantage of longitudinal research is that it controls for the cohort (or history) effect. As you read, an age cohort is a group of people born the same year. A cohort effect is said to occur when a group of people is different due not to age, but to a common historical event which affected all of the people at that age (what is called a normative history-graded influence, in your textbook). A common example of a cohort effect is the Vietnam War. During the 1960's and early 70's, young people were much more interested in politics and less supportive of the status quo than were their parents. A cross-sectional design would have suggested that this is age-related, as people get older, they become less politically active. However, young people in the 1980's and 1990's are not nearly as politically involved as the previous generation. An alternative hypothesis is that when political decisions really meant life or death to young people (that is, they could get sent to Vietnam), and there was a situation that appeared very unfair to them (they were old enough to fight and possibly be killed in Vietnam but not old enough to vote), then people become more politically active. A longitudinal design would have found that people who were young adults in the 1950's or 1980's were not that politically active, and therefore conclude that the difference probably wasn't developmental,but due to a difference in the history experienced by people who were young adults in 1968 as opposed to middle-aged or older.

While the author of your textbook doesn't seem too positive about case study research (and, it is true that many people do not consider it as scientific as methods using large groups), it is a fact that many times you as a teacher, nurse or psychologist will be interested in explaining the behavior of a specific individual. Many important developments in psychology have been based, at least in part, on case studies, for example, Freud's analyses of individual patients and Piaget's observations of his own three children.

It is the best method for determining causality, that is, whether one variable causes another to change. It works like this:
 

1. 1 A random sample is taken from the population of interest (e.g., fourth graders, middle-aged adults, children of alcoholics, etc.)
2. 2 Subjects (the people you selected) are randomly assigned to one of two groups, the experimental or control group. It is not a good experiment if you assign all the really intelligent, healthy subjects to one group and all the really dumb, sick subjects to the other.
3. 3 You manipulate an independent variable (whatever it is that you want to determine if it has an effect).
4. 4 You measure the dependent variable (whatever it is that you think will be caused to change)
5. 5 You use inferential statistics to see whether any differences that exist between the experimental and control group could be due to chance. (It is extremely rare for two groups to ever be EXACTLY equal on any variable, whether it is height, weight, behavior problems, IQ or whatever. This is called random variance. People just differe from one another and two groups of people are expected to differ somewhat from each other. Inferential statistics provide the probability that differences between two groups are more than you would expect by chance.)

You randomly select 100 children aged 3-5 years (#1).

You randomly assign the children to an experimental or control group (#2)

The experimental group watches Kung-Fu films for 20 minutes. At the end, they are given M & M's and sent out to play.
The control group waits in the waiting room for 20 minutes, then are told they are not needed for the experiment, but are given M & M's for their time in waiting (#3 - watching the films or not is the independent variable).

The number of times children hit, push, shove, kick, etc. other children is counted (#4 the dependent variable is the number of times they are involved ina physical conflict).

Finally, you would compare these two groups to see if the differences were more than would be expected to exist between any two groups of children.

Why don't psychologists always do experiments, if it is such a good method? Well, because we can't. It is impossible, for example, to randomly assign children to be either
Abused or non-abused                                            Poor or middle-class
From a family with an alcoholic parent or not         Male or female

So, for many factors which affect development, true experiments are not possible, which is why many methods of research are needed.

Click here for assignment # 1

Click here to go on to the next lesson, describing another common research method in psychology

Click here to return to the previous lesson

Click here to send email with questions, your response to assignment #1 or just generally tell me how much  you like the course.