A large-scale clinical trial was conducted to assess the effect of carvedilol (a mixed alpha- and beta-blocker) on the clinical course of New York Heart Association class III-IV chronic heart failure. The study reported that serum noradrenaline levels (a marker of the degree of neurohumoral activation) were correlated with serum sodium levels with correlation coefficient r = -0.39 (p = 0.005). Which of the following statements best describes the observed relationship between serum noradrenaline levels and serum sodium levels?

Question

A large-scale clinical trial was conducted to assess the effect of carvedilol (a mixed alpha- and beta-blocker) on the clinical course of New York Heart Association class III-IV chronic heart failure.  The study reported that serum noradrenaline levels (a marker of the degree of neurohumoral activation) were correlated with serum sodium levels with correlation coefficient r = -0.39 (p = 0.005).  Which of the following statements best describes the observed relationship between serum noradrenaline levels and serum sodium levels?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c0f5_b003_8f63_db2664a37960_MD0005_00 Correlation coefficient (r) values range from -1 to 1. The sign indicates a positive or negative direction of linear association between 2 variables; the null value is 0, which denotes no association. The closer the r value is to its margins [-1, 1], the stronger the association. In this study, the correlation coefficient is negative (r = -0.39), meaning that a negative linear association exists between serum noradrenaline levels and serum sodium levels. As a result, serum noradrenaline levels would be expected to increase as serum sodium levels decrease. This statement does not imply a causal relation between the 2 levels; it only indicates that an increase in one level is associated with a decrease in the other. (Choice B) A positive correlation would imply that serum noradrenaline levels increase as serum sodium levels increase. This is not the case in this study. (Choices C and D) In this study, the correlation coefficient (r = -0.39) is statistically significant (p = 0.005), but the association is weak because its value is closer to 0 than to 1. (Choice E) The correlation coefficient shows the strength of the association but does not imply causality. Educational objective: The correlation coefficient shows the strength and direction (positive or negative) of linear association between 2 variables but does not imply causality.

A Large-Scale Clinical Trial Was Conducted to Assess the Effect