Finding a Critical F-Value for a Two-Tailed Test In Exercises 9–12, find the critical F-value for a two-tailed test using the level of significance α and degrees of freedom d.f.N and d.f.D.

α=0.01, d.f.N=6, d.f.D=7

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Step 1: Understand the problem. You are tasked with finding the critical F-value for a two-tailed test. The level of significance (α) is 0.01, and the degrees of freedom for the numerator (d.f.N) is 6, while the degrees of freedom for the denominator (d.f.D) is 7.

Step 2: Recognize that for a two-tailed test, the level of significance (α) is split equally between the two tails of the F-distribution. This means each tail will have an area of α/2 = 0.01/2 = 0.005.

Step 3: Use an F-distribution table or statistical software to find the critical F-values. For the upper critical value, locate the value corresponding to α/2 = 0.005, d.f.N = 6, and d.f.D = 7. For the lower critical value, take the reciprocal of the upper critical value (1/F_upper).

Step 4: If using an F-table, find the row corresponding to d.f.N = 6 and the column corresponding to d.f.D = 7 under the α/2 = 0.005 column. This gives the upper critical F-value. For the lower critical value, calculate 1/F_upper.

Step 5: Summarize the results. The critical F-values for the two-tailed test are the lower critical value (1/F_upper) and the upper critical value (F_upper). These values define the rejection regions for the test.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

F-Distribution

The F-distribution is a probability distribution that arises frequently in statistics, particularly in the context of variance analysis. It is used to compare variances between two populations and is defined by two sets of degrees of freedom: one for the numerator (d.f.N) and one for the denominator (d.f.D). The shape of the F-distribution is right-skewed, and it is important for hypothesis testing in ANOVA and regression analysis.

Critical Value

A critical value is a threshold that determines the boundary for rejecting the null hypothesis in hypothesis testing. For a two-tailed test, critical values are found at both ends of the distribution, corresponding to the chosen level of significance (α). In this case, with α = 0.01, the critical values will be located in the extreme 0.5% of each tail of the F-distribution, indicating the regions where the null hypothesis can be rejected.

Degrees of Freedom

Degrees of freedom (d.f.) refer to the number of independent values or quantities that can vary in an analysis without violating any constraints. In the context of the F-test, d.f.N represents the degrees of freedom associated with the numerator (the group or treatment variances), while d.f.D represents the degrees of freedom associated with the denominator (the error or residual variances). These values are crucial for determining the critical F-value from the F-distribution table.

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