A researcher conducts an experiment using 10 loads of white shirts with similar stains. The loads are divided, and 5 of the loads are washed with name-brand detergent, while the other 5 are washed with store-brand detergent. Volunteers are asked to assess the cleanliness of the shirts.
What are the experimental units in this setting?
the types of detergent
the 10 loads of shirts
the volunteers who assess the stains
the machines used to wash the shirts