Question

Collect the price of five vegetables from your local market every day for a week. Calculate their correlation coefficients. Interpret the result.

Answer 1

Day	Potato (per kg)	Tomato (per kg)	Onion (per kg)	Babycorn (per kg)	Broccoli (per kg)
1	18	30	35	110	170
2	18	35	36	112	165
3	18	32	35	120	150
4	20	32	34	118	155
5	20	35	36	115	155
6	20	35	35	110	160
7	21	32	35	111	165

Correlation between prices of potato and tomato 

Potato (per kg) (x)	Tomato (per kg) (Y)	`X -overlineX`	`(X -overlineX)^2`	`Y -overlineY`	`(Y -overlineY)^2`	`(X -overlineX)` `(Y -overlineY)`
18	26	-1	1	-4	16	4
18	31	-1	1	1	1	-1
18	28	-1	1	-2	4	2
18	28	-1	1	-2	4	2
20	31	1	1	1	1	1
20	35	1	1	5	25	5
21	31	2	4	1	1	2
∑X =  133	∑Y = 210		∑`(X -overlineX)^2` = 10		`(Y -overlineY)^2 = 52`	∑`(X -overlineX)` `(Y -overlineY)` = 15

r = `(sum(X - overlineX)(Y - overlineY))/sqrt(sum(X - overlineX)^2(Y - overlineY)^2` = +0.65

Likewise we can calculate correlation between different pairs of vegetables or we can use multivariate correlation to find the relation between the vegetables.