Learn moreLearn moreApplied Statistics Handbook

Table of Contents



Comparing the mean incomes of high school graduates and high school dropouts from 1993 survey data.



Two-Sample Difference of Means



Independent Variable: EduCat        Education Level

Dependent Variable: Income  Respondent individual income


Sample One: 1 <12 yrs

Sample Two: 2 HS Grade


                         Sample 1         Sample 2

                         <12 yrs          HS Grade


Sample Mean              23042.5000       31000.8235

Std Deviation             4450.5413        9442.4477

Sample Size (n)              6                17



                        Homogeneity of Variance


              F-ratio   5.08     DF (16, 5)   p < 0.0408 A



                  T-statistic          DF     p < (2-tailed)


Equal Variance         -1.9660        21            0.0627 B

Unequal Variance       -2.7220        21.67         0.0124 C






A   The F-ratio is statistically significant. Use the unequal variance test statistic.

B   For a 2-tailed test, the p-value represents the probability of making a type 1 error (concluding there is statistical significance when there is none).  Since there is about 1.2% (p < .0124) chance of making a type 1 error, which does not exceed the 5% error limit (p=.05, alpha), you conclude there is statistical significance.

C   If you had not checked for homogeneity of variance, you would have erroneously failed to find statistical significance. 




Copyright 2015, AcaStat Software. All Rights Reserved.