Item Analysis
Item Analysis
Item Analysis
Item Analysis is the group of statistics that can be computed for each item on a test.
Distractor Analysis
How many persons chose each distractor?
Were the distractors effective?
Examine the total pattern of responses to each item
Item Difficulty
How many persons answered the item correctly?
Item Discrimination
To what extent does the item discriminate between these who are
knowledgeable about the content and those who are not? i.e.
Discrimination between those who do well and those who do poorly on
the test.
Distractor Analysis
Based on the number of persons who chose each incorrect response or distractor
on a multiple choice item.
Those who know will choose correct answer.
Those who don’t know should choose equally among distractors if all
distractors are equally effective.
No. expected to choose each distractor: no. who answered incorrectly
no. of distractors
Item Difficulty
This is the proportion of persons who are able to get the item right. A test item
should not be so easy that everyone gets it right, neither should it be so difficult
that no one chooses the correct response.
This gives the item difficulty index, which is a value ranging between 0 and 1.
0 – Very difficult (no one got it right) 1.00 – Very easy (everyone got it
right)
An item difficulty of 0 or 1.00 means that the test does not discriminate.
Item Discrimination
D = Up - Lp
U- L
Because U and L are the same, the formula changes to:
D = Up-Lp
U
Up – No. of persons in the upper 27% or 33% (the high performing group) who got
the item correct.
Lp – Persons in the lower 27% or 33% (the low performing group) who got the
item correct
U – Total number in the high performing group
L – Total number in the low performing group
NB. Note that you may choose any percentage within the range of 27% to 33% to
determine how many test-takers will comprise each group
The item discrimination index is a value ranging between 0 and 1. 0 means that the
item does not discriminate at all (the upper and lower performing group did equally
well on the item), while 1 means that it discriminates extremely well (everyone in
the high performing group got the item right, while no one in the low group got it
right). The higher the value of D, the more effective is the item at discriminating
between high and low scorers/performers.
Conclusion
Those items that do not have good difficulty or discriminatory power can be
discarded or reconstructed.