A group of sixty newly diagnosed diabetic patients were tested for anxiety using a standardized inventory. They were retested for anxiety again after months using the same inventory. The mean difference in anxiety was evaluated by a suitable t-test. The degrees of freedom associated with the t-test would be

1. A120
2. B118
3. C59
4. D58

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Correct answer: C. 59

Explanation

The same 60 patients are tested twice (paired/dependent t-test), so df = n − 1 = 59.