Is there an association between level of happiness and the risk of heart disease? Researchers studied 1739 people over a 10 year period and asked questions about their daily lives and the hassles they face. The researchers also determined which individuals in the study experienced any type of heart disease. After their analysis, they concluded that happy individuals are less likely to experience heart disease. (Source: European Heart Journal 31 (9):1065–1070, February 2010.)

Correlation is a statistical measure of co-movement relationship between two variables. It denotes whether the two variables move in same or opposite direction.

Positive Correlation : Variables move in same direction. One variable increase, other variable increase & one variable decrease, other variable decrease.
Negative Correlation : Variables move in opposite direction. One variable increase, other variable decrease & one variable decrease, other variable increase

The research study of happiness & heart disease depicts that these variables are negatively correlated, as : Higher the happiness level , lower the risk of heart disease & lower the happiness level, higher the risk of heart disease.