# Cross-Sectional Designs: Definition & Examples

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Lesson Transcript
Instructor: Devin Kowalczyk

Devin has taught psychology and has a master's degree in clinical forensic psychology. He is working on his PhD.

This lesson explores the process and requirements in using a cross-sectional design. Two examples are used, one common and one uncommon, to demonstrate how cross-sectional designs can be used in quasi-experiments.

## Cross-Sectional Designs: Definition and Advantage

Have you ever wondered why little kids are so weird? They just do bizarre things sometimes. If you have kids, I'm sure they're wonderful, but other peoples' kids? They have problems. The thing is, not all children are weird in the same way. Some eat things; some throw things; some just sit there and whisper secrets from beyond space and time. What, just me?

So, what does this weird kid story have to do with anything? Well, if you're ever interested in studying the differences as a child develops and matures, then you have two options: a longitudinal study, which will be explored in another lesson, and a cross-sectional study.

Cross-sectional designs are sampled groups taken and examined from a continuum to determine if there is a difference between different sections of the continuum. This is, unfortunately, a little vague because different continuums can be used. For instance, if you made \$100,000 a year, and I made \$10,000 a year, then there is likely to be differences between us.

Usually, the continuum is age, but sometimes you may want to study other things that can be larger or smaller. This is a quasi-experiment, defined as not a true experiment, because it uses naturally formed groups rather than randomly assigned ones. Remember, a true experiment must have randomly assigned groups so that everyone has an equal chance of being in the experimental or the control group. Why is a cross-sectional experiment not a true experiment? Simply put, you cannot assign people to age categories. You as a researcher cannot assign your participants to be three years old, five years old, and eight years old. Life and time don't work that way.

Okay, enough bad jokes. Cross-sectional designs are used to examine how people change over time by using representatives from different age categories. This allows you to do an experiment and look to see the differences between a five-year-old, a 10-year-old, and a 15-year-old all in one experimental run instead of working over 10 years to complete this one experiment. This is one of the advantages offered by a cross-sectional design; you don't have to worry about losing your entire sample group as time passes or what might happen over the years because your entire experiment is completed in one test run. We will discuss two uses of a cross-sectional design to illustrate how they are used.

## Example 1

How quickly do speech and verbal skills develop? For a researcher to study this, we would need to take a cross-sectional sample of a group of young kids. Specifically, we need to look at a large group of kids, their specific ages, and a series of tests dealing with speech and verbal skills.

Why do we need a large group? We as researchers need to control for individual differences. Some children will speak at a very young age, while others are delayed. Having a large group helps us control for some of the variability.

Why do we need specific ages? If we are dealing with any type of group, we need to clearly define them. We want each group to be exclusive, so that there isn't any overlap. In this experiment, we could differentiate age by months or even number of days. However, if we were to differentiate ages by something as broad as years, then we would have fewer groups. Remember, the focus of this experiment is on speech and verbal skill development, so we need to focus on talking as it develops instead of after it has reached a plateau.

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