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Introduction Correlation is the measurement to measure how two datasets increase or decrease together. It's a real number range from -1 (i.e, when one dataset increases, another one decreases and vice versa) to +1 (i.e, these two datasets increase or decrease together). Value 0 means there is no relationship between two datasets. Calculating correlation Calculating correlation of two datasets in R is quite straightforward: In R: > x = c (1,5,2,6,7) > y = c (2,4,3,9,-5) > cor(x,y) [1] -0.1459338 Usually, a single value does not say much in statistics. You need a confidence level. > cor.test (x, y) Pearson's product-moment correlation data: x and y t = -0.2555, df = 3, p-value = 0.8149 alternative hypothesis: true correlation is not equal to 0 95 percent confidence interval: -0.9109173 0.8451475 sample estimates: cor -0.1459338 The function 'cor.test' will gives you the correlation, and also 95% confidence level of