Experiments
Learning Outcomes
- Identify methods for obtaining a random sample of the intended population of a study
- Identify ineffective ways of obtaining a random sample from a population
- Identify types of sample bias
- Identify the differences between observational study and an experiment
- Identify the treatment in an experiment
- Determine whether an experiment may have been influenced by confounding
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.
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 testAnswer: a. Observational study
b. Experiment; the treatment is the jumping jacks
c. Experiment; the treatments are coffee and tea
