A study done in 2013 examined people with clinical depression and evaluated other aspects of their physical health. The research found that people with clinical depression were more likely to have autoimmune diseases such as hashimoto’s and rheumatoid arthritis than people without clinical depression. Based on the researchers, these results strongly support the hypothesis that mental states influence the body’s immune system.

Which of the following, if true, casts the most serious doubt on the researchers’ interpretation of their findings?

1. The researchers’ view does little more than echo a familiar theme in folklore and literature.
2. Clinically depressed individuals are no less careful than others to follow a healthy lifestyle. 
3. Disorders of the immune system cause many of those individuals who have them to become clinically depressed.
4. Individuals who have previously been free from depression can become depressed quite suddenly.
5. A high frequency of autoimmune disorders can stem from an unusually high level of exposure to stress. 

OA: C 

Question type: Weaken

Difficulty level: Medium

Summary of the argument: Being clinically depressed makes people more likely to develop autoimmune disorders; this is based on the correlation found in the study. 

1. This is irrelevant and not true based on the argument. 
2. This actually strengthens the argument by removing an alternate cause. 
3. This is correct as it shows a reverse causation. Perhaps people with autoimmune disorders are more likely to develop depression and not the other way round. 
4. This does not relate to the context of autoimmune disorders. 
5. “Stress” is vague and out of scope.

X