Improve your assessment skills by this

1. IMPROVING
THE TEST
ITEMS

2. ITEM ANALYSIS
is the process
of evaluating
the quality of
the items and
of the tests as
a whole.
“investigates the
performance of
items considered
individually in
relation to the
remaining items
on the test”
(Thompson &
Leviton, 1985).
It is the
process of
examining
the pupil’s
responses to
each test
item.

3. “U-L INDEX METHOD (Stocklein,
1957)
(Upper-Lower Index Method)

4. The most commonly used U-L Index Method is the
Upper and Lower 27%.
1. Score the papers and rank them from highest to lowest according to total
score.
2. Separate the top 27% and the bottom 27% of the papers.
3. Tally the responses made to each test item by each individual in
the upper 27% group.
4. Tally the responses made to each test item by each individual in
the lower 27% group.
5. Compute the percentage of the upper group that got the item right
and call it U.

5. 6. Compute the percentage of the lower
group that got the item right and call it L.
7. Average U and L percentage and the result is
the difficulty index of the item.
8. Subtract the L from the U percentage and the
result is the discrimination index of the item.

6. Item difficulty/difficulty index
▸It can be interpreted as
how easy or how difficult
an item is. The larger the
percentage getting an
item right, the easier the
item. The higher the
difficulty index, the easier
the item is understood to
be.
Difficulty index,
denoted by p, is
simply the
percentage of
the students
taking the test
who answered
the item
correctly.

7. ▸For example, an item answered correctly by 85% of the
examinees will have an item difficulty of .85, whereas an
item answered by 50% of the examinees would have a
lower item difficulty of .5.
▸It is usually best when difficulty index is around .5, for it
provides maximum differentiation.
▸The best difficulty index, however, is halfway between
the lowest and highest expected score. When all of the
items are extremely difficult, the great majority of the test
scores will be very low. When all items are extremely
easy, most test scores will be extremely high
Item difficulty/difficulty index

8. We do not want
items that are too
easy or too
difficult.

9. Itemdiscrimination/discriminationindex
▸The discriminative power of a
test item, denoted by D refers to
the degree of the ability of an item
to distinguish those who know
from those who do not know.
▸It can be measured by comparing
the number of people with high test
scores who answered that item
correctly with the number of
people with low scores who
answered the same item correctly.
A good item
discriminates
between those
who do well on
the test and those
who do poorly
(Susan Matlock-
hetzel, 1997).

10. ▸The top and bottom 27% are used for analysis because 27% has
shown that this value will maximize differences in the normal
distribution while providing enough cases for analysis (Wiersma and
Jurs (1990). Other methods use 30% while others use 50% (no middle
group).
▸The higher discrimination index, the better the item because such a
value indicates that the item discriminates in favor of the upper group,
which should get more items correct.
▸If more students in the lower group get an item correct than in the
upper group, the item will have a negative D value and is probably
flawed.
▸Similarly, if there are equal number of students from the upper
group and lower group, the item cannot discriminate because D value
is 0.
Itemdiscrimination/discriminationindex

11. Computing for the difficulty
index and discrimination index of
an item is a lot easier than
interpreting it. Remember that the
purpose of the analysis is to
determine which are good items;
that is there are items to be
retained or accepted, rejected or
discarded, and revised.

12. Range of Difficulty Index (p) Interpretation
0 - .20 Very difficult
0.21 – 0.40 Difficult
0.41 – 0.60 Moderately difficult
0.61 – 0.80 Easy
0.81 – 1.00 Very easy
Table for interpreting difficulty index (p)

13. Range of Discrimination Index (D) Interpretation
-1.0 - -.06 Questionable
-0.59 - -0.20 Not discriminating
-0.21 - 0.20 Moderately discriminating
0.21 - 0.60 Discriminating
0.61 - 1.00 Very discriminating
Table for interpreting discrimination index (D)

14. In interpreting the results, we have to
consider not only whether how easy or
how difficult the item is, but also its
ability to discriminate students who
know and those who do not know the
answer. In other words, both the p
values and D values are taken into
consideration. The decision rule is to
retain or accept the items that are not
so easy or too difficult, and at the same
time can discriminate bright from poor
students.

15. After interpreting the difficulty and discrimination indices, the
table below will help us what to do with the test item
Difficulty Index Discrimination Index Suggested Action
Difficult
Not discriminating Discard/Reject
Moderately discriminating May need revision
Discriminating/Very
discriminating
Accept/Retain
Moderately difficult
Not discriminating Needs revision
Moderately discriminating May need revision
Discriminating/Very
discriminating
Accept/Retain
Easy
Not discriminating Discard/Reject
Moderately discriminating Needs Revision
Discriminating/Very
discriminating
Needs Revision

16. Note that whether an item is easy,
moderately difficult or difficult, there are
always three categories of
discrimination indices that can be
obtained, that also leads to three
different actions. For example, an easy
item could either be not discriminating,
moderately discriminating or
discriminating, and then it could be
rejected, revised or retained.

17. The table below shows a sample result of an item analysis, illustrating the
steps of the U-L Index method..
Study the results and focus on the interpretation of the test item.
Table showing a summary of the Item Analysis
Item
No.
Upper
27%
Lower
27%
U L p Interpretation D Interpretation Action
1 14 12 .88 .75 .82 Very easy .13 Moderately
discriminating
Revise
2 10 6 .63 .38 .51 Moderately
difficult
.25 Discriminating Retain
3 11 7 .69 .44 .57 Moderately
difficult
.25 Discriminating Retain
4 9 2 .56 .13 .35 Difficult .43 Discriminating Retain
5 12 6 .75 .38 .57 Moderately difficult .37 Discriminating Retain
6 6 14 .38 .88 .63 Easy -.50 Questionable Discard
7 13 4 .81 .25 .53 Moderately difficult .56 Discriminating Retain
8 3 10 .19 .63 .41 Moderately difficult -.44 Questionable Discard
9 13 12 .81 .75 .78 Easy .06 Moderately
discriminating
Revise
10 8 6 .50 .38 .44 Moderately difficult .12 Moderately
discriminating
Revise
Number of students tested - 60

18. Step 1. The papers have been scored and arranged from
highest to lowest
Step 2. There were 60 students who took the test, so 27% of
60 is 16. Therefore, there are 16 students from the
upper group and another 16 students for the lower group.
The middle group (28 students) will not be included in the
analysis.
Step 3. The number of students from the upper group was
tallied. For example, out of 16 students, 14 students got
item 1 correctly, 10 students for item 2, and so forth.
Step 4. The number of students from the lower group was
tallied. For example, out of 16 students, 12 students got
item 1 correctly, 6 students for item 2, and so forth.

19. Step 5. The percentage of the students from the upper group is
obtained by dividing the number of students who got the item right and
the total number of students; that is 14/16 = .88, or 88%., 10/16 = .63
or 63 % for item 2, and so forth. The results are placed under Column
U (upper group)
Step 6. The same procedure like in step 5 was performed. For
example, 12/16 = .75 0r 755 for item 1, and so forth. Results are
placed under Column L (lower group)
Step 7. The difficulty index (p) was computed by getting the average
of U and L percentages. For example in item 1 U = .88, L = .75.
Therefore, p = (U+L)/2 = (.88+.75)/2 = .82. This means that 82 % of
the students got item 1 correctly.
Step 8. The discrimination index (D) is obtained by subtracting L from
U, that is D = U – L, or D = .88 - .75 = .13

20. So for item number 1, the difficulty index is .82
and the discrimination index is .13. Using the
tables presented earlier, a difficulty index of .82
is said to be very easy, and a discrimination
index of .13 is moderately discriminating. The
item therefore needs revision. The item was
too easy because there were many students,
even from the lower group who got the item
correctly.