Example 3: Comparison of 2 frequencies

You received two batches from two different suppliers.  The red parts represent the defective parts. The defect rate of supplier A is 2/24 and defect rate of supplier B is 5/30. With the data at your disposal, can you say that supplier a is significantly better than supplier B?

Exemple 3

Which test should you choose ?

Enter the data in Ellistat.  Then select the Inferential statistics menu (on the left). In the adapted test menu (table on top), select the two columns containing your Y data (here supplier a and supplier B).

The inappropriate tests will become greyed out and the only choice left will be the 2P test.


Choix test

Left hand table- Depending on the comparison to be carried out: We want to compare the defect frequency between the two samples, therefore we use test 2P.

Right hand table – Depending on the types of variables:Y is  the result of the OK/KO measurement (qualitative), dependant (X) on the kind of supplier, A or B (qualitative), therefore the comparison requires a 2P test.

Result :

Enter the data from the 2 samples in the corresponding boxes.


The difference between the two samples is not significant. This means that supplier A can not be considered to produce significantly fewer defects than supplier B. Contrary to our intuition, supplier A is not necessarily better than supplier B.