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TUTORIAL 8
Question 1: Why is it important for a teacher to analyse each of
the test item?
1. Fix marksfor current class that just wrote the testo
find flaws in the test so that you can adjust the mark before
return tostudents
o can find questions with two right answers, or that were too
hard, etc., thatyou may want to drop from the exam
2. More diagnostic informationon studentso another immediate
payoffof item analysis
Classroom level:
o will tell which questions they were are all guessing on, or if
you find aquestions which most of them found very difficult, you
can reteach thatconcept
o CAN do item analysis on pretests to: so if you find a question
they all got right, don't waste more time on
this area
find the wrong answers they are choosing to identify
commonmisconceptions
can't tell this just from score on total test, or class
average
Individual level:
o isolate specific errorsthis child made
o after you've planned these tests, written perfect questions,
and nowanalyzed the results, you're going to know more about these
kids thanthey know themselves
3. Build future tests, revise test items to make them bettero
REALLYpays off second time you teach the same course
by now you know how much work writing good questions is
studies have shown us that it is FIVE times faster to revise
itemsthat didn't work, using item analysis, than trying to replace
it with acompletely new question
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new item which would just have new problems anyway
--> this way you eventually get perfect items, the envy of
yourneighbours
o SHOULD NOT REUSE WHOLE TESTS--> diagnostic teaching
meansthat you are responding to needs of your students, so after a
few yearsyou build up a bank of test items you can custom make
tests for your class
know what class average will be before you even give the
testbecause you will know approximately how difficult each itemis
before you use it;
can spread difficulty levels across your blueprint too.
4. Part of your continuing professional developmento doing the
occasional item analysis will help teach you how to become a
better test writer
o and you're also documenting just how good your evaluation
is
o useful for dealing with parents or principals if there's ever
a dispute
o once you start bringing out all these impressive looking stats
parents and
administrators will believe that maybe you do know what you're
talkingabout when you fail students...
o parent says, I think your "question stinks",
well, "according to the item analysis, this question appears to
have workedwell "
(actually, face validity takes priority over stats any day!)
o and if the analysis shows that the question does stink, you've
already
dropped itbefore
you've handed it back to the student, let alone the parentseeing
it.
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Question 2: What is the item difficulty for the following
situations?
a. Thirtty students take a test and only twenty answered item 1
correctly.
20/30 = 0.67
b. All the students in (a) answered item 2 correctly.
30/30 = 1
c. None of the ss answered item 3 correctly.
0/30 = 0
The item difficulty index is calculated as
percentage of the total number of correct responses to
the test item. It is calculated using the formula
P=R/T, where P is the item difficulty index, R is the
number of correct responses and T is the total number
of responses (which includes both correct and incorrect
responses). An item was considered difficult when the
difficulty index value was less than 30% and the item
was considered easy when the index value was greater
than 80%.
Si-Mui Sim, Rasiah RI. Relationship between item difficulty
anddiscrimination indices in true/false type multiple choice
questions of
a para-clinical multidisciplinary paper. Ann Acad Med
Singapore
2006; 35: 67-71
