How to find F critical value in R:

To determine the F critical value R provides us qf() function whose syntax is given below:

Syntax:

qf(p, df1, df2,lower.tail=TRUE)

Parameters:

• p: It represents the significance level to be used
• df1: It represents the numerator degrees of freedom
• df2: It represents the denominator degrees of freedom
• lower.tail = TRUE: Then the probability to the left of p in the F distribution is returned.
• lower.tail = TRUE: Then the probability to the right is returned.
• Note that by default lower.tail is TRUE.

Return Type:

Returns the critical value from the F distribution on the basis of the significance level, numerator degrees of freedom, and denominator degrees of freedom provided.

Example:

Let us consider an example in which we want to determine the F critical value for a significance level equal to 0.01, numerator degrees of freedom equal 4, and denominator degrees of freedom = 6.    

Output:

Interpretation of output:

Hence, the F critical value for a significance level of 0.01, numerator degrees of freedom equal to 4, and denominator degrees of freedom equal to 6 comes out to be equal to 9.14830103022785.

Therefore, if a particular type of F test is conducted then we can compare the F test statistic with 9.14830103022785. If the F statistic turns out to be more than 9.14830103022785, then the results of the test are considered statistically significant.

When the F test is conducted we get the F statistic as an outcome. In order to determine whether the outcome of an F test is statistically significant or not, the F statistic is compared with an F critical value. If the F-statistic comes out to be greater than F critical value then the results of the test are considered statistically significant.

For finding F critical value, we need to have the following information beforehand:

• significance level (common choices are 0.01, 0.05, and 0.10)
• Numerator degrees of freedom
• Denominator degrees of freedom