47
4.2 Computation Between the Two Means
Mean is the average value of the scores. In order to know the significant difference of the experiment could be seen through the difference of the two
means.
N xe
Me Σ
=
N xc
Mc Σ
=
Where: Me : the mean scores of the experiment group
Xe Σ
: the sum of all scores of the experiment group Mc : the mean scores of the control group
xc Σ : the sum of all scores of the control group
N : the number of the subject sample The computation of the scores of the experiment group and control group
was calculated as follows:
N xe
Me Σ
=
20 1544
= = 77.20
The mean score of the experiment group was 77.20
N xc
Mc Σ
=
= 20
1380
48
= 69.00 The mean score of the control group was 69.00
If we compared the two means it was clear that the mean of the experiment group was higher than that of the control group. The difference between the two
means was 8.20. To make the analysis more reliable, t-test formula was used.
⎟ ⎠
⎞ ⎜
⎝ ⎛
+ ⎟
⎠ ⎞
⎜ ⎝
⎛ −
+ +
− =
Nc Ne
Nc Ne
Ssc Sse
Mc Me
t 1
1 2
Where t : t-test
Me : the mean difference of the experiment group Mc : the mean difference of control group
Sse : sum of quadrate deviation of the experiment group Ssc : sum of quadrate deviation of the control group
Ne : the number of experiment group Nc : the number of control group
For applying the t-test formula above, we must to find Sse and Ssc first. To find Sse and Ssc, the formula is:
Ne xe
xe Sse
2
Σ −
Σ =
Nc xc
xc Ssc
2
Σ −
Σ =
From the formula and based on the data in appendix 12, the writer can find the deviations of each value of the experiment and control group are:
49
Ne xe
xe Sse
2
Σ −
Σ =
20 1544
119696
2
− =
= 20
2383936 119696
− = 119696 – 119196.8
= 499.20 The deviation of each value of the experiment group is 499.20
Nc xc
xc Ssc
2
Σ −
Σ =
=
20 1380
95920
2
−
=
20 1904400
95920 −
= 95920 – 95220 = 700.00
And the deviation of each value of the control group is 700.00. After the writer got the Sse and ssc, then she calculated the t-test. The
result is:
⎟ ⎠
⎞ ⎜
⎝ ⎛
+ ⎟
⎠ ⎞
⎜ ⎝
⎛ −
+ +
− =
Nc Ne
Nc Ne
Ssc Sse
Mc Me
t 1
1 2
=
⎟ ⎠
⎞ ⎜
⎝ ⎛
+ ⎟
⎠ ⎞
⎜ ⎝
⎛ −
+ +
−
20 1
20 1
2 20
20 00
. 700
20 .
499 00
. 69
20 .
77
50
=
⎟ ⎠
⎞ ⎜
⎝ ⎛
⎟ ⎠
⎞ ⎜
⎝ ⎛
20 2
38 20
. 1199
20 .
8
=
1 .
56 .
31 20
. 8
=
16 .
3 20
. 8
=
78 .
1 20
. 8
= 4.616
4.3 Test of Significance