Independence test is a statistical test, which belongs to X2 test and also belongs to fitness test, that is, chi-square test, which is a hypothetical test to judge whether two factors are related or independent according to frequency data.

Calculate the value of random variable k 2 (that is, the square of k) from the data in the joint table. The greater the value of k 2, the more likely it is that "X and Y are related".

The learning goal of independence test: to understand the basic idea of independence test; The focus of the independence test: the independence of two classified variables will be tested.

That is why we can't just draw a conclusion from the data in the contingency table and the diagram it draws? We can roughly estimate whether two variables (two objects) are related by contingency table (that is, roughly carry out independence test), but the data in 2×2 contingency table is sample data, which only represents the population and is random. We need to use independence test to confirm the extent to which the conclusion applies to the population. This point will be further illustrated in later cases.

In order to prove conclusion A, we want to explain that the hypothesis H 1 (two classified variables, that is, two objects are related) holds. Reasoning on the premise that A is not established, and reasoning on the condition that H 1 is not established, that is, H0 (two objects are independent of each other) is established, and deducing the contradiction means that conclusion A is established.

It is concluded that a small probability event (the probability is not greater than α, α is generally 0.00 1, 0.0 1, 0.05 or 0. 1) occurs, indicating that the possibility of H 1 is very high (the possibility is 1-α), and no contradiction is found.