7.202 STATS_F_TEST
Syntax
Purpose
STATS_F_TEST
tests whether two variances are significantly different. The observed value of f is the ratio of one variance to the other, so values very different from 1 usually indicate significant differences.
This function takes two required arguments: expr1
is the grouping or independent variable and expr2
is the sample of values. The optional third argument lets you specify the meaning of the NUMBER
value returned by this function, as shown in Table 75. For this argument, you can specify a text literal, or a bind variable or expression that evaluates to a constant character value. If you omit the third argument, then the default is 'TWO_SIDED_SIG'
.
See Also:
Appendix C in Oracle Database Globalization Support Guide for the collation determination rules for STATS_F_TEST
Table 75 STATS_F_TEST Return Values
Argument  Return Value Meaning 


The observed value of f 

Degree of freedom for the numerator 

Degree of freedom for the denominator 

Onetailed significance of f 

Twotailed significance of f 
The onetailed significance is always in relation to the upper tail. The final argument, expr3
, indicates which of the two groups specified by expr1
is the high value or numerator (the value whose rejection region is the upper tail).
The observed value of f is the ratio of the variance of one group to the variance of the second group. The significance of the observed value of f is the probability that the variances are different just by chanceāa number between 0 and 1. A small value for the significance indicates that the variances are significantly different. The degree of freedom for each of the variances is the number of observations in the sample minus 1.
STATS_F_TEST Example
The following example determines whether the variance in credit limit between men and women is significantly different. The results, a p_value not close to zero, and an f_statistic close to 1, indicate that the difference between credit limits for men and women are not significant.
SELECT VARIANCE(DECODE(cust_gender, 'M', cust_credit_limit, null)) var_men, VARIANCE(DECODE(cust_gender, 'F', cust_credit_limit, null)) var_women, STATS_F_TEST(cust_gender, cust_credit_limit, 'STATISTIC', 'F') f_statistic, STATS_F_TEST(cust_gender, cust_credit_limit) two_sided_p_value FROM sh.customers; VAR_MEN VAR_WOMEN F_STATISTIC TWO_SIDED_P_VALUE     12879896.7 13046865 1.01296348 .311928071