Cochran’s test for equality of variances

Apply Cochran s test for equality of variances to Example 1.38. 

In the case where there are k populations and the test of equality of population variances is required, the most commonly applied test is the Cochran s test for homogeneity of variances. 

The tabular value X9.0 975=19.0 is considerably higher than the arithmetic so that with a 95% probability one can assert that the variances are equal. A simpler and more frequently used test for equality of variances is Cochran s test. 

If the arithmetic of Cochran s test is below the tabular value, the null hypothesis that variances are equal is accepted. Tabular values are in Table I and are determined for the associated threshold or significance level a=0.05 and degree of freedom fi=n-l number of data used in calculating the variance sf is reduced by one, or in other words the number of replicated design points (trials) is reduced by one and the f2-number of variances or number of trials. 

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