Group Statistics |
|
Survey_Credit |
N |
Mean |
Week2 |
0 -- Survey Not Completed |
5 |
3.60 |
5 -- Survey Completed |
15 |
6.93 |
As you can see, those students who completed the survey
did much better on the quiz than did those who did not. Of course, this
difference could be due to chance alone, even if in the larger population there
were no relationship between survey participation and performance on a quiz.
Independent Samples Test |
|
t-test for Equality of Means |
t |
df |
Sig. (2-tailed) |
Mean Difference |
Std. Error Difference |
95% Confidence Interval of the
Difference |
Lower |
Upper |
|
|
-3.368 |
18 |
.003 |
-3.333 |
.990 |
-5.413 |
-1.254 |
|
Were there no relationship between survey
completion and quiz performance, the chances of getting, in the sample, a
difference between groups as large as that observed here would be only 3 in
1,000. This is strong evidence that those who take the time to contribute
to class by completing a survey perform better on quizzes in the class than do
those who do not take the time to complete a survey.
|
So,
why this association between completing the survey and doing well on the quiz?
It is, IMHO, unlikely that completing the survey has any causal relationship
with quiz performance. The association between taking the survey and doing
well on the quiz is likely due to both of these being causally related to a
third variable. In this case, that third variable is what I call GaF.
Scoring high on Gaf causes one to complete the survey and also causes one to
study the material and then do well on the quiz. I am working on a device
to measure GaF. A prototype is shown below.
|