Question 2: How does a negative correlation between CHQ-C and NYHA provide evidence for criterion validity?
CHQ-C is intended to measure quality of life in patients with congestive heart failure. The NYHA classification focuses on limitation of activity. Clearly, the higher the NYHA classification the poorer will be the subjectís quality of life and NYHA can act as a criterion for CHQ-C. As NYHA IV is the lowest quality of life, we expect a negative correlation with CHQ-C if CHQ-C is valid.
A rank correlation coefficient is used because NYHA is an ordinal variable.
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