Learning Outcomes
- Identify the differences between observational studies and experiments
Read with a pencil in hand
Continue to read these sections with a pencil in hand. Make note of definitions, but also make note of keywords that will help you to identify an observational study versus an experiment. Work the TRY IT and EXAMPLES out by hand to gain the experience you’ll need to correctly identify these on a test.
What you’ll learn to do: Examine the methods for sampling and experimentation and how bias can affect the results
As we mentioned previously, the first thing we should do before conducting a survey is to identify the population that we want to study. In this lesson, we will show you examples of how to identify the population in a study, and determine whether or not the study actually represents the intended population. We will discuss different techniques for random sampling that are intended to ensure a population is well represented in a sample.
We will also identify the difference between an observational study and an experiment, and ways experiments can be conducted. By the end of this lesson, we hope that you will also be confident in identifying when an experiment may have been affected by confounding or the placebo effect, and the methods that are employed to avoid them.
Observing vs. Acting
So far, we have primarily discussed observational studies – studies in which conclusions would be drawn from observations of a sample or the population. In some cases these observations might be unsolicited, such as studying the percentage of cars that turn right at a red light even when there is a “no turn on red” sign. In other cases the observations are solicited, like in a survey or a poll.
In contrast, it is common to use experiments when exploring how subjects react to an outside influence. In an experiment, some kind of treatment is applied to the subjects and the results are measured and recorded.
Observational studies and experiments
- An observational study is a study based on observations or measurements
- An experiment is a study in which the effects of a treatment are measured
Examples
Here are some examples of experiments:
A pharmaceutical company tests a new medicine for treating Alzheimer’s disease by administering the drug to 50 elderly patients with recent diagnoses. The treatment here is the new drug.
A gym tests out a new weight loss program by enlisting 30 volunteers to try out the program. The treatment here is the new program.
You test a new kitchen cleaner by buying a bottle and cleaning your kitchen. The new cleaner is the treatment.
A psychology researcher explores the effect of music on temperament by measuring people’s temperament while listening to different types of music. The music is the treatment.
These examples are discussed further in the following video.
Try It
Is each scenario describing an observational study or an experiment?
a. The weights of 30 randomly selected people are measured
b. Subjects are asked to do 20 jumping jacks, and then their heart rates are measured
c. Twenty coffee drinkers and twenty tea drinkers are given a concentration test
This is the end of the section. Close this tab and proceed to the corresponding assignment.
