Reason for conducting an experiment
An experiment looks for a causal relationship between a response and one or more explanatory variables.
Experimental units
Experiments are generally conducted on a set of experimental units. Depending on the type of experiment, these units could be people, animals, trees, areas in a field, shops in a retail chain, ...
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. These controlled characteristics are explanatory variables and are called factors in the context of an experiment. The different values of the controlled characteristics are called experimental treatments.
Experimental design
The decision about which treatment is applied to each experimental unit is called the experimental design.