- Review an experiment and explain if it has been designed well
- Use randomized block design to create a hypothetical experiment to answer a research question
Well-Designed Experiments
The primary goal of an experiment is to provide evidence for a cause-and-effect relationship between two variables.
- Factor of interest: The explanatory variable (independent variable), which is what we suspect has an effect on the response variable.
- Response factor/variable: The dependent variable, which we suspect is affected by the factor of interest.
In an experiment, the researcher manipulates values of the explanatory variable and measures the resulting changes in the response variable. The different values of the explanatory variable are called treatments.
treatments
Treatments are experimental conditions into which the participants are divided, some into a group receiving the treatment of interest and others into a control group that does not receive the treatment (a placebo).
A placebo is a harmless version of the treatment that does not contain any active ingredients (e.g., a sugar pill). The placebo will typically look, taste, and smell like the treatment of interest or mimic it so that the two treatments appear identical to the subjects; this way the subjects don’t know which treatment they are receiving.
experimental unit
The single object or individual to be measured in the experiment is called an experimental unit. The experimental units of the whole experiment are split into two groups:
- One group receives the treatment of interest (this is usually called the experimental group) and the other group does not.
- The group that does not receive the treatment of interest or the placebo is the control group.
placebo effect
The placebo effect is a positive response from people who believe they are receiving treatment for a condition when they are actually receiving a placebo.
The placebo effect can make it difficult to gauge the effects on the response variable. It is a fascinating connection between mind and body that is still not completely understood.