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.
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