Final answer:
When a researcher divides subjects into groups based on ethnicity for an experimental study, it is known as stratified sampling, ensuring subgroups of the population are adequately represented.
Step-by-step explanation:
A researcher dividing experimental subjects into several groups based on their ethnicity is using stratified sampling in experimental design. Stratified sampling is a method where the population is divided into different subgroups or strata, and then a simple random sample is taken from each of these strata to ensure that each subgroup is adequately represented.
This approach can be particularly useful when researchers want to make sure that specific characteristics such as age, class, race, or education are proportionately represented in the sample. The goal is to produce a sample that is a microcosm of the larger population, which can increase the validity of the experiment's conclusions. An example of stratified sampling would be a health club wanting to know typical member attendance, thus they survey every tenth customer from different member demographics on a given day.