ITEM ANALYSIS

It is a statistical technique which is used for selecting and rejecting the items of the test on the basis of their difficulty value and discriminated power.

ITEM ANALYSIS

Try-out phaseItem analysis phaseItem revision phase

Phases of preparing a test

Two characteristics of an item:

Item DifficultyDiscrimination Index

Item Difficulty“The difficulty value of an item is defined as

the proportion or percentage of the

examinees who have answered the item

correctly”

- J.P. Guilford

I.D = no. of students with the correct ans.

total number of students

Example:

What is the item difficulty index of an item if 25 students are unable to answer it correctly while 75 answered it correctly?

Range of difficulty

index

Interpretation Action

0 – 0.25 Difficult Revise or discard

0.26 – 0.75 Right difficulty retain

0.76 - above Easy Revise or discard

General guidelines for difficulty value (D.V)

Low difficulty value index means, that item is high difficulty one ex: D.V=0.20 » 20% only answered correctly for that item. So that item is too difficult

High difficulty value index means, that item is easy one

ex: D.V=0.80 » 80% answered correctly for that item. So that item is too easy one

“Index of discrimination is that ability of an

item on the basis of which the discrimination

is made between superiors and inferiors”

- Blood and Budd (1972)

Index of Discrimination

Types of discrimination index (D.I)

Zero discrimination or No discrimination

Positive discrimination

Negative discrimination

Index Range Interpretation Action

-1.0 to -.50 Can discriminate but the item is questionable

Discarded

-.55 to .45 Non-discriminating

Revised

.46 to 1.0 Discriminating item

Include

STEPS in getting I.D

Arrange the scores in descending order

Separate two sub groups of the test papers

Get 25% of the scores out of the highest

scores and 25% falling at bottom

Count the number of students who got

answer correctly in both groups.

Discrimination index = DU – DL

Example: Consider a multiple item choice type of test with the ff. data were obtained:

Item Options

1A B* C D

0 40 20 20 Total

0 15 5 0 Upper 25%

0 5 10 5 Lower 25%

The discrimination index can be similarly be computed:

DU = no. of students in the upper 25% with correct response

No. of students in the upper 25%

=15/20 = .75 or 75%

DL= no. of students in lower 75% with correct response

no. of students in the lower 25%

= 5/20 = .25 or 25%

Discrimination index = DU – DL

= .75 - .25

= .50 or 50%`

FORMULAS

Index of Difficulty

P= RU + RL

T

Index item Discriminating Power

D= RU + RL

½ T

100

100

Relationship between difficulty value and discrimination power

Both (D.V & D.I) are complementary not

contradictory to each other

Both should considered in selecting good items

If an item has negatively discriminate or zero

discrimination, is to be rejected whatever the difficulty

value

Criteria for selection and rejection items

Positive discrimination index only selected

Negative and zero discrimination index items

are rejected

High and low difficulty value items are

rejected