Glucose measurement, answer 3

Question 3: What does the correlation coefficient tell us about the agreement between capillary glucose and laboratory glucose?

Suggested answer:

The correlation coefficient tell us nothing about the agreement between capillary glucose and laboratory glucose. It tells us how closely they are related. A correlation r = 0.98 tells us that the two are closely related, but completely ignores the overall bias, an average difference = 0.36 mmol/L, which was statistically significant from 0, P = 0.007. Furthermore, this bias depends on the magnitude of the glucose. For small glucose, capillary glucose overestimates relative to laboratory glucose, for large glucose capillary glucose underestimates relative to laboratory glucose.


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