These designs examine what changes and what stays the same in a human life. Chronological age, cohort membership, and time of measurement are the basic elements of research designs looking at development. The frustrating thing about doing this kind of research is that you only can vary two of these three elements at a time. The two that you choose will determine the third element. Therefore no single study can definitively tell you about how human beings develop. However, combining results of multiple studies and using more complex designs, such as cross-sequential designs, can help us get closer to the truth.
Cross-sectional research involves beginning with a sample that represents a cross-section of the population. Respondents who vary in age, gender, ethnicity, and social class might be asked to complete a survey about television program preferences or attitudes toward the use of the Internet. The attitudes of males and females could then be compared as could attitudes based on age. In cross-sectional research, respondents are measured only once. This method is much less expensive than longitudinal research but does not allow the researcher to distinguish between the impact of age and the cohort effect. Different attitudes about the Internet, for example, might not be altered by a person’s biological age as much as their life experiences as members of a cohort.
Longitudinal research involves beginning with a group of people who may be of the same age and background, and measuring them repeatedly over a long period of time. One of the benefits of this type of research is that people can be followed through time and be compared with them when they were younger. A problem with this type of research is that it is very expensive and subjects may drop out over time. (The film 49 Up is a example of following individuals over time. You see how people change physically, emotionally, and socially through time.) What would be the drawbacks of being in a longitudinal study? What about 49 Up? Would you want to be filmed every 7 years? What would be the advantages and disadvantages? Can you imagine why some would continue and others drop out of the project?
Cross-sequential research involves combining aspects of the previous two techniques; beginning with a cross-sectional sample and measuring them through time. This is the perfect model for looking at age, gender, social class, and ethnicity. But here the drawbacks of high costs and attrition are here as well.
the amount of time elapsed since an individual’s birth, typically expressed in terms of months and years.
a group of individuals who share a similar characteristic or experience. The term usually refers to an age (or birth) cohort, that is, a group of individuals who are born in the same year and thus of similar age.
the moment in time when the participants' responses are recorded.
a research design in which individuals, typically of different ages or developmental levels, are compared at a single point in time. An example is a study that involves a direct comparison of 50-year-olds with 80-year-olds. Given its snapshot nature, however, it is difficult to determine causal relationships using a cross-sectional design. Moreover, a cross-sectional study is not suitable for measuring changes over time, for which a longitudinal design is required.
the study of a variable or group of variables in the same cases or participants over a period of time, sometimes several years. An example of a longitudinal design is a multiyear comparative study of the same children in an urban and a suburban school to record their cognitive development in depth. A longitudinal study that evaluates a group of randomly chosen individuals is referred to as a panel study, whereas a longitudinal study that evaluates a group of individuals possessing some common characteristic (usually age) is referred to as a cohort study.
a study in which two or more groups of individuals of different ages are directly compared over a period of time. It is thus a combination of a cross-sectional design and a longitudinal design. For example, an investigator using a cross-sequential design to evaluate children’s mathematical skills might measure a group of 5-year-olds and a group of 10-year-olds at the beginning of the research and then subsequently reassess the same children every 6 months for the next 5 years.