The Difficulty Level of the Test Discriminating Power

3.8.1 The Difficulty Level of the Test

According to Heaton 1975:172, “ the index of difficulty or the facility value of an item simply shows how easy or difficult the particular item proved in the test. ” An item is considered to have a good difficulty level if it is not too easy or too difficult for the students, so they can answer the items. If a test contains many items, which are too difficult or too easy, it cannot function as a good means of evaluation. Therefore, every item should be analyzed first before it is used in a test. The formula of item difficulty is as follows: P = Where: P : Item difficulty B : Number of students who answered the item correctly JS : Number of students Arikunto, 1995:212

3.8.2 Discriminating Power

It is also essential to determine the discriminating power of the test items because it can discriminate between the more and the less able students. Heaton 1975:173 states “ The discrimination index of an item indicated the extent to which the item discriminated between the testers, separating the more able testers from the less able. The index of discriminating told us whether those students who performed well on the whole test tended to do well or badly on each item in the test ” . Js B There are various methods of obtaining the index of discrimination; here the writer applied the procedure favored by Heaton 1975:175 as follows: First, the writer counted the number of the students on the upper and lower groups who answered the item correctly. Then, she subtracted the number of students giving correct answers in the upper group, and found the difference in the proportion passing in the lower group. Then, she divided the difference by the total number of candidates in one group. The procedure of calculating the discriminating power explained above could be expressed by the following formula: D = Where: BA : Number of students in the upper group who answered the item correctly. BB : Number of students in the lower group who answered the item correctly. JA : Number of all students in the upper group. JB : Number of students in the lower group. Arikunto, 1995:218 The classification of the discrimination index is presented below: D : 0,00 – 0,20 = Poor D : 0,21 – 0,40 = Satisfactory D : 0,41 – 0,71 = Good D : 0,71 – 1,00 = Excellent

3.9 Method of Collecting the Data