Reason for conducting an experiment
An experiment is usually conducted in order to determine how some response is affected by one or more types of potential influences.
An experiment looks for a causal relationship between a response and one or more explanatory variables.
For example, a researcher may wish to determine...
Experimental units
Experiments are generally conducted on a set of experimental units. Depending on the type of experiment, these units may be...
In the experiments that we will examine here,...
A single response measurement is made from each experimental unit.
Factors and treatments
The researcher has control over some aspect of each unit — perhaps a numerical characteristic such as the temperature at which a plant is grown or a categorical characteristic such as the variety of plant that is planted.
These controlled characteristics are the explanatory variables and are called factors in the context of an experiment. The different values of the controlled characteristics are called experimental treatments.
Each experimental unit receives some treatment.
Experimental design
The decision about which of the different treatments is applied to each experimental unit is called the experimental design.