Question

select the correct answer.

a company wants to test a new brand of dog food that has added omega-3 oils for healthy, shiny coats.

the company selects two groups of volunteers who have dogs as pets. they give each person in both groups a months supply of dog food. each bag of dog food is unlabeled. one group is given the dog food with the added omega-3 oils, and the other group is given a brand of dog food without the added omega-3 oils. both groups are asked to feed their dogs the food the company gave them and report whether they noticed an improvement in their dogs coats.

which statement is correct?

• the experiment is blinded because the volunteers in both groups and the company are all unaware of which group received the dog food with omega-3 oils.
• the experiment is blinded because the volunteers in both groups are unaware of which dog food they received.
• the experiment is not blinded because the volunteers in both groups are aware of which type of dog food they received.
• the experiment is not blinded because the volunteers in both groups and the company are all unaware of which group received the dog food with omega-3 oils.

Explanation:

Analyze the experimental setup

The study describes an experiment where a company tests a new dog food with added omega-3 oils. Two groups of volunteers are given a month's supply of dog food. Crucially, the text states: "Each bag of dog food is unlabeled." This means the volunteers do not know which version of the dog food (with or without omega-3 oils) they are feeding to their dogs.

Define blinding in experiments

In statistics and experimental design, an experiment is blinded (specifically single-blinded) if the subjects (or in this case, the volunteers evaluating the dogs' coats) do not know which treatment group they belong to. This prevents subjective bias when they report whether they noticed an improvement in their dogs' coats.

Evaluate the options

• Option 1: Claims the experiment is blinded because both the volunteers and the company are unaware. This describes a double-blind study. However, there is no indication in the text that the company itself is unaware of which group received which food (the company distributed the foods to the groups). Thus, we cannot assume it is double-blinded.
• Option 2: Claims the experiment is blinded because the volunteers in both groups are unaware of which dog food they received. This is correct because the bags are unlabeled, preventing volunteer bias.
• Option 3: Claims the experiment is not blinded. This is incorrect because the unlabeled bags ensure the volunteers are unaware, which constitutes blinding.
• Option 4: Claims the experiment is not blinded because both groups and the company are unaware. This is logically contradictory (if they were unaware, it would be blinded).

Answer:

• The experiment is blinded because the volunteers in both groups and the company are all unaware of which group received the dog food with omega-3 oils.
• The experiment is blinded because the volunteers in both groups are unaware of which dog food they received. (Correct answer)
• The experiment is not blinded because the volunteers in both groups are aware of which type of dog food they received.
• The experiment is not blinded because the volunteers in both groups and the company are all unaware of which group received the dog food with omega-3