f tests Determine if Variances are the Same
You Don't Have to be a Statistician to Perform an f tests on Your Data
f test Example
If you're producing rubber made with two different recipes, you might want to know if the variances in tensile strengths are the same or different (Juran's QC Handbook 4th pg 23.74):
- The null hypotheis (H0) - variances are the same
- The alternate hypothesis (Ha) - variances are different
The QI Macros for Excel Makes f tests as Easy as 1-2-3
- Enter your data in Excel, then click and drag over the data to select it. Next click on the QI Macros Menu, Statistical Tools and then select the F test:
- The QI Macros will prompt for a significance level (default = 0.05):
- The QI Macros will perform the f test calculations and interpret the results for you.
What's Unique about QI Macros f-Test Calculations?
When you run the f-Test, you don't have to think. Unlike other statistical software, the QI Macros is the only SPC software that compares the p-value (0.152) to the significance level (0.05) and interprets the result for you. "Cannot Reject the Null Hypothesis because p>0.05" and that the "Variances are the same." Based on the f test results we now know which t test to run.
Interpreting the F test results
|Classical Method||test statistic > critical value
(i.e. F > F crit)
|Reject the null hypothesis|
|Classical Method||test statistic < critical value
(i.e. F < F crit)
|Cannot Reject the null hypothesis|
|p value Method||p value < a||Reject the null hypothesis|
|p value Method||p value > a||Cannot Reject the null hypothesis|
Since F < Fcrit (.33 < 6.39) and p value > a ( .152 > 0.05), we cannot reject the null hypothesi - the Variances are the Same.
If you run the test using, Excel's Data Analysis toolpak, Excel requires that the recipe with the largest variance be first to ensure correct calculations. The QI Macros does not have this requirement to perform the calculations correctly.
Not Sure Which Statistical Test to Run?
The QI Macros Stat Wizard will analyze your data and choose the right hypothesis tests for you. Just select your data, click on the QI Macros and then Stat Wizard.
The QI Macros Statistical Software for Excel includes these statistical tests and tools:
Tests of Variances: Anova One Way, Anova Two Way Without Replication, Anova Two Way With Replication, f-Test Two Sample for Variances, Levene's Test for non-normal variances
Test of Means: t-test One Sample, t-test Two-Sample Assuming Equal Variances, t-test Two-Sample Assuming Unequal Variances, t-test Paired Two-Sample for Means, z-test Two-Sample for Means, Two One-Sided Test for Equivalence
Tests of Relationships: Chi-square Contingency Table, Chi-square Goodness of Fit, Correlation
Covariance, Descriptive Statistics, Exponential smoothing, Fisher Exact Test, Multiple Regression Analysis, Regression Analysis.
And More: Normality Test, Sample Size Calculator, Test of Proportions, Non-Parametric Tests, Tukey Quick Test
Why Choose the QI Macros Over Other Statistical Programs?
Ease of Use
- QI Macros Stat Wizard will analyze your data and run all possible statistical tests for you.
- Works right in Microsoft Excel
- PC - Excel 2000 to 2013 and Office 365
- Mac - Excel 2011 and Office 365
- Mistake proofs data selection and formatting issues.
- Output interprets the results for you.
- Just $229 per license and less with Quantity Discounts