Page 151 - DEDU504_EDUCATIONAL_MEASUREMENT_AND_EVALUATION_ENGLISH

Unit 10 : Item Analysis : Item Difficulty, Discrimination index, Effectiveness of Distractors

Step 5 : The teacher records the responses on the whiteboard as follows : Notes
High Low Total of Correct Answers
Question # 1 14 8 22
Question # 2 12 6 18

Question # 3 16 7 23
|
|
Question # n n n n
Step 6 : Compute the Difficulty Index for Question # 1 as follows :
+
R+R L 14 8
H
Difficulty Index = = = 0.73
30 30
Step 7 : Compute the Discrimination Index for Question # 1 as follows :
−
R − R 14 8 6
Discrimination Index = H L = = = 0.40
½30 15 15
Note that earlier, we took 27% of answer sheets in the ‘High Marks’ group and 27% of answer
sheets in the ‘Low Marks’ group from the total answer sheets. However, in this approach we
divided the total answer sheets into two groups. There is no middle group. The important thing
is to use a large enough fraction of the group to provide useful information. Selecting the top and
bottom 27 per cent of the group is recommended for more refined analysis. This method may be
less accurate but it is a ‘quick and dirty’ method.
Self Assessment

2. Fill in the blanks :
(i) ______ is a basic measure which shows the extent to which a question discriminates
between students in the High marks groups and Low marks group.
(ii) For calculating discriminating value of an item by the formula method, the answer books
are arranged in a definite ______ order.
(iii) 27% Top and 27% bottom right response method was mentioned by ______.
(iv) ______ provide a theoretical model to explain the relationship between difficulty index
and discrimination index.

10.12 Summary

• According to Lamark, “The procedure used to judge the quality of an item is called item-
analysis.”
• The chief objective of item-analysis of a test is to select those items which are suitable,
reliable and valid for that class of students or individuals for whom the test has been
constructed. A good test requires.
• In brief, item-analysis is needed for the following purposes :
(i) Rejecting the items which are weak and have double meaning.
(ii) Each selected item should represent the whole test.
(iii) Determining the number of items to be included in the test.

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