1.4 - Research Study Design

Experimental and Observational Designs Section

Research studies are often classified in terms of their designs. Here, we will make the distinction between experimental and observational research designs.

Experimental Research Design

A study in which the researcher manipulates the treatments received by subjects and collects data; also known as a scientific study

Observational Research Design

A study in which the researcher collects data without performing any manipulations; also known as a non-experimental study

Example: Caffeinated Coffee Studies Section

Coffee cup

An organization wants to know if drinking caffeinated coffee causes hyperactivity in college students. To test their research question, they select a sample of college students and give them a survey concerning their intake of caffeinated coffee and their hyperactivity levels. This is an observational study because the researchers are not making any manipulations. They are observing what is happening without intervening. This is not an experiment because no treatment was imposed by the researchers.

Another organization also wants to know if drinking caffeinated coffee causes hyperactivity in college students. They design a different study. They select a random sample of college students and randomly assign them to drink coffee with or without caffeine. The researchers observe the students' behaviors. This is an experimental study because a treatment is being imposed. The researchers are manipulating the treatment that each participant receives.

On Your Own Section

A team of researchers want to know if Advil or Tylenol is more effective.

Think about the following data collection methods, then click on the method to compare your answers.

Method 1
Researchers survey a sample of adults and ask if they use Advil or Tylenol. They ask them to rate the effectiveness of the one they use. Is this an observational study or experimental study?
This is an observational study because the researchers observed the difference between two existing groups (Advil and Tylenol users). The researchers did not manipulate the participants' experiences. 
Method 2
Researchers obtain a random sample of adults. They randomly assign half of the participants to take Advil and the other half to take Tylenol. They ask each participant to rate the effectiveness of the one that they were assigned to take. Is this an observational study or experimental study?
This is an experimental study because the researchers assigned participants to groups.