According to Ardhana (in Yasril, 1998: 50), to test difference between two means is used t-test formula:
In calculating S2 (estimate value of population variance) is using formula:
The degrees of freedom is n1 + n2 – 2 at the level of significance () 0.05. There is a significant difference if tratio > ttable.
The steps in calculating the t-test are arranged as bellow:
1. Count the estimate value of variance of the population
220109 - (2953)2 + 173970 – (2700)2
= 42 45
42 + 45 – 2
= 287.7056
2. Count the difference between two means, mean of the class with portfolio assessment and mean of the class with traditional assessment. The result is called as tratio
= 70.3059 – 60
287.7056 + 287.7056
42 45
= 10.3059
3.6392
= 2.833
3. Count the ttable than compare it with tratio
The degrees of freedom is n1 + n2 – 2 = 42 + 45 – 2 = 85 at the level of significance () 0.05. ttable = t ( 1 - ½ ) = t ( 1 – 0.025 )
For df = 85, t 0.975 = 1.992
tratio compare with ttable tratio = 2.833 > ttable = 1.992.
From this result, it means that there is a significant difference between the students’ learning achievement with traditional assessment and portfolio assessment.
Appendix 9
Examples of Portfolio
