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