The Missouri Reader Vol. 36, Issue 1 | Page 74

Table 1. Paired Samples t-Test for Strategic Ability
Paired Samples Test
Paired Differences
95% Confidence Interval of
the Difference

Mean
Pair 1 preability postability

Std.
Std. Error
Deviation Mean
Lower

Upper

t

df

Sig. (2-tailed)

-3.33333

4.07840

-1.47687

-3.745

20

.001

.88998

-5.18980

Table 2. Pre- and Post- Means for Strategic Ability
Paired Samples Statistics
Mean

Std. Deviation

Std. Error Mean

preability

23.8571

21

5.44321

1.18781

postability

Pair 1

N

27.1905

21

3.82909

.83558

A paired-samples t-Test was calculated to compare the mean pretest score (Pre-Perception Survey) to the mean posttest score (PostPerception Survey). The mean on the pretest was 23.86 (sd = 5.44), and the mean on the posttest was 27.19 (sd = 3.83). A significant
increase from pretest to posttest was found (t(20) = 3.75, p‹.05). The SPSS calculated value of p (probability of making a Type I error)
was 0.001.

Effect Size
In order to determine the effect size, the following formula was used from Glass and Hopkins (1996):
M2 – M 1
SD2 + SD1

M2=Posttest Mean

M1=Pretest Mean

SD2=Posttest Standard Deviation

SD1=Pretest Standard Deviation

2

Using the means and standard deviation with the above formula the effect size was calculated to be 0.72. That is over 2/3 of a standard
deviation shift. This shows a strongly moderate effect on the change in student perceptive ability (Gay, Mills, & Airasian, 2009). For
example, if the group perceived that they were able to perform at 50% during the pretest, their perception after the conduction of the
posttest would be at 74%.
© The Missouri Reader, 36 (1) p.74