# 卡方检验

## chi2test

Usage: [p, Q]= chi2test(x)

The chi-squared test.

Given a number of samples this function tests the hypothesis that the samples are

independent. If Q > chi2(p, nu), the hypothesis is rejected.

Each column represents a variables, each row a sample.

If you find any errors, please let me know: .

ARGUMENTS:

x Absolut numbers.

p The prob ability value, calculated from Q.

Q The resulting Q-value.

EXAMPLE 1

In region A, 324 of 556 cows were red, whereas in region B 98 of 260 were red.

[p, Q]= chi2test([324, 556-324; 98, 260-98])

p= 4.2073e-08

Q= 30.0515

With an error risk of about 4e-08, we can claim that the samples are independent.

EXAMPLE 2

Throw two different dices to see if they have the same probability of 1 (and 2, 3, 4, 5, 6).

We don't check if they are symetrical, only if the both behave in the same way.

[p,Q] = chi2test([15,10; 7,11; 9,7; 20,15; 26,21; 19,16])

p= 0.8200

Q = 2.2059

The dices don't significantly behave differently. That is, they seem to behave in the same way.

HISTORY: v.1.0, first working version, 2007-08-30.

COPYRIGHT: (c) 2007 Peder Axensten. Use at own risk.

chi2test.zip (1.85KB)

chi2test.m