Statistically, correlation coefficient is used to quantitatively describe the strength and direction of linear correlation between two variables. For example, two interrelated variables, one increasing and one decreasing, are positively related in the same direction of change. For example, two interrelated variables, one increasing and the other decreasing, are negatively correlated. The correlation coefficient is r,? R takes the value from-1 to+1. The absolute value of correlation coefficient r represents the correlation strength between two variables; The sign of correlation coefficient r indicates the direction of correlation, which is positive correlation and negative correlation respectively; Correlation coefficient? R=0, called zero linear correlation, referred to as zero correlation; When the correlation coefficient |r|= 1, it means that the two variables are completely correlated. When 0.7 ≤| r | < 1, it is called high correlation; When 0.4 ≤| r | < 0.7, it is called moderate correlation; When 0.2 ≤| r | < 0.4, it is called low correlation; When | r |r|