Observational Studies: Learn It 1

learning GOALS

  • Explain why observational studies are used.
  • Explain what a confounding variable is in an observational study.
  • Explain the difference between an experimental study and an observational study.

In the next activity, you will learn about observational studies and learn to distinguish between experiments and observational studies.

You previously learned about experiments, or experimental studies. An experimental study is a statistical study based on data collected from designed experiments and is useful for determining cause and effect. In such a study, a treatment is imposed by the researcher to allow for a comparison between groups. In this What to Know page, you’ll learn how to distinguish between experimental studies and observational studies.

Observational Studies

In an observational study, a researcher will observe an outcome without changing who is and who is not exposed to some sort of treatment. Instead of trying to assess cause and effect, an observational study is typically used when the goal is to learn about characteristics of a population or to compare groups within a population with respect to some characteristic. Sometimes observational studies are preferred over experimental studies because they might be the only way certain types of questions can be studied. Observational studies may allow a researcher to avoid assigning participants of a study to a treatment that would be considered unethical. However, due to lack of control and assignment to a treatment, observational studies may inherently be at risk of containing confounding biases, which are outside of the control of the researcher. A confounding variable is a variable that was not accounted for in a study and may actually influence other variables in a study.

Video Placement

[Perspective Video: a 3-instructor video that previews all the ideas on this page — experiment vs observational study, confounding variables, and why observational studies are necessary (i.e., why experiments would sometimes be unethical to conduct.]

Now you try to answer some questions about an observational study. For Questions 1–4, consider the following scenario.

A researcher wants to explore how smoking habits relate to depression. She has a group of self-described smokers take a survey and assign a numerical value to describe their level of depression. The survey also asks participants to record their heights, weights, and ages. Similarly, she has a group of self-described non-smokers take the same survey.

question 1

1) In this study, level of depression, height, weight, and age are all ____________.

  1. a) populations
  2. b) samples
  3. c) variables

question 2

2) This is an observational study because _____________.

  1. a) the researcher assigns each participant to the smoking or non-smoking group
  2. b) the researcher collects information from the participants without assigning a treatment

question 3

3) Determine whether this statement is true or false: When studying the relationship between smoking habits and depression, an observational study is best since it would be unethical to force participants to begin smoking.

question 4

4) Determine whether this statement is true or false: Based on the responses, the researcher notes that several of the smokers also reported higher weights than the non-smokers. Weight may be a confounding variable in this study.