A nurse is interested in whether there is a relationship between daily levels of stress and likelihood of a heart attack. The stress scores (predictor variable) and risk of heart attack values (criterion variable) from a small sample of participants are depicted below.(Values below are valid for this question only!)

Stress ScoreRisk of Heart Attack

(Higher values = morestress)(Higher values = greater risk)

02

28

30

87

What is the standard deviation of the criterion variable?