Page 58 - Contributed Paper Session (CPS) - Volume 4

CPS 2126 Dr. Rajkumari Sanatombi Devi et.al
determining difficulty in objective examination. The proportion of passing an
item is an index of item difficulty. If 90% of a standard group pass an item, it
is easy; if only 10% pass, the item is hard. Discrimination index also known as
validity of the test items or point biserial correlation is the other parameter
used in item analysis. Item discrimination determines whether those who did
well on the entire test did well on a particular test’s item. The size of an
acceptable validity index will depend upon the length of the test, the range of
the difficulty indices, and the purposes for which the test is designed (Garrette,
1966). Fowell et al., (1999) Discrimination index (DI) describes the ability of an
item to distinguish between high and low scorers. Discrimination index (DI),
ranges between -1.00 and +1.00. It is expected that the high-performing
students select the correct answer for each item more often than the low-
performing students. If this is true, the assessment is said to have a positive DI
(between 0.00 and +1.00), indicating that students who received a high total
score, chose the correct answer for a specific item more often than the
students who had a low overall score. If, however, the low performing students
got a specific item correct more often than the high scorers, then that item
has a negative DI (between -1.00 and 0.00). Garrette (1966) as a general rule,
items with validity indices of 0.20 or more are regarded as satisfactory, but
items with lower indices will often serve if the test is long. Item having zero
validity are, of course, useless. These items and items having negative validity
(a larger percent right in the bottom group than the top) must be discarded;
or they must be carefully examined for ambiguities, inaccuracies and other
errors. Carroll (1993) the difficulty and discrimination indices are often
reciprocally related. However, this may not always be true. Questions having
high p-value (easier questions), discriminate poorly; conversely, questions with
a low p-value (harder questions) are considered to be good discriminators. In
the present study, the definition of Difficulty index (DIF I) given by Frank S.
Freeman defined as the proportion of certain sample of subjects who actually
know the answer of an item was used. Index of difficulty for each test item can
be calculated as

DIF I = (Ru + Rl) / (Nu + Nl)
DIF I = item difficulty
Ru = the number of students in the upper 27% who responded correctly
Rl = the number of students in the lower 27% who responded correctly
Nu = the number of students in the upper group
Nl = the number of students in the lower group
The difficulty index (DI) for an item was categorizes as followed

Cut off point of Difficulty index (Dif I) Quality of item
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