How much two variable related each other.
always use correlation in statistic.
x= 3, 4, 5
y= 8, 5, 3
r = Σi[(xi-x)(yi-y)] / √Σi[(xi-x)(yi-y)]
x=1/N Σ Xi
y=1/N Σ Yi
x-x -1, 0, 1
y-y 3, 0, -3
= -6 / √ 2 * 18
= -1
x= 3, 4, 5
y= 8, 5, 8
r= 0
x= 3, 4, 5 xμ = 4
y= 8, 3, 7 yμ = 6
x-x -1, 0, 1
y-y 2, -3, 1
= -1 / √ 2 * 14
= -0.189
