Do Now What percent of Americans wash their hands after using the bathroom? It depends on how collect data. In a telephone survey of 1006 U.S. adults 96% said they always wash their hands after using a public restroom. An observational study of 6028 adults in public restrooms told a different story: Only 85% of those observed washed their hands after using the restroom. Explain why the results of the two studies are so different.

Observational Studies and Experiments Lesson 3.6 Observational Studies and Experiments

Objectives Explain the concept of confounding and how it limits the ability to make cause-and-effect conclusions. Explain the purpose of comparison in an experiment. Describe the placebo effect and the purpose of blinding in an experiment.

Confounding Variables Placebo effect Control Group Single-blind Confounding Variables Can’t say this is causation

Definitions Confounding occurs when 2 variables are associated in such a way that their effects on a response variable cannot be distinguished from each other. A treatment is a specific condition applied to the individuals in an experiment. The experimental units are the smallest collection of individuals to which treatments are randomly assigned. When the units are human beings, they are often called subjects. In an experiment, a control group is a group used to provide a baseline for comparing the effects of other treatments.

Definitions The placebo effect describes the fact that some subjects in an experiment will respond favorably to any treatment, even an inactive treatment. A placebo is a treatment that has no active ingredient, but is otherwise like other treatments.

Definitions In a double-blind experiment, neither the subject nor those who interact with them and measure the response variable know which treatment a subject received. In a single-blind experiment, either the subjects don’t know which treatment they are receiving or the people who interact with them and measure the response variable don’t know which subjects are receiving which treatment.