One hundred volunteers who suffer from severe depression are available for a study. Fifty are selected at random and are given a new drug that is thought to be particularly effective in treating severe depression. The other 50 are given an existing drug for treating severe depression. A psychiatrist evaluates the symptoms of all volunteers after 4 weeks in order to determine if there has been substantial improvement in the severity of the depression. In which situation would this study be double blind?

1. If neither the volunteers nor the psychiatrist knew which treatment any person had received

2. If all volunteers were not allowed to see the psychiatrist nor was the psychiatrist allowed to see the volunteers during the session when the psychiatrist evaluated the severity of the depression

3. All of the above

4. If neither drug had any identifying marks on it

The correct option is 1: If neither the volunteers nor the psychiatrist knew which treatment any person had received

Step-by-step explanation:

Consider the provided information.

Fifty are selected at random and are given a new drug and the other 50 are given an existing drug for treating severe depression. A psychiatrist evaluates the symptoms of all volunteers after 4 weeks in order to determine if there has been substantial improvement in the severity of the depression.

An experiment is said to be a double-blind study if the crucial aspects of the experiment are not revealed to either participants or experimenters

Now use the above definition to identify the correct option.

Option 1. If neither the volunteers nor the psychiatrist knew which treatment any person had received.

This option is correct because neither the participants or experimenters know the crucial aspects of the experiment.

Option 2, 3 and 4 are not correct as they don't interpret the correct meaning of double blind study.

Hence, option 1 is correct.