Item Analysis

ITEM ANALYSIS

ITEM DIFFICULTY 

It is defined as the number of  students who are able to answer the item correctly divided by the total number of students.

INDEX OF DISCRIMINATION 

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Tells whether it can discriminate between those who know and those who do not know the answer. It is the difference between the proportion of the upper group who got an item right and the proportion of the lower group who got the item right.

RANGE OF DIFFICULTY INDEX INTERPRETATION

ACTION

0-0.25

Difficult

Revise or discard

0.26-0.75

Right difficulty

Retain

0.76above

Easy

Revise or Discard

RANGE

RANGE OF DIFFICULTY INDEX RANGE

INTERPRETATION

ACTION

-1.0 --0.50

Can discriminate but item is questionable

Discard

-.55--0.45

Non discriminating

Revise

0.46-1.0

Discriminating item

Include

BENEFITS DERIVED FROM ITEM  ANALYSIS 

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It provides useful information for class discussion of the test It provides data which helps students improve their learning It provides insights and skills that lead to the preparation of better tests in the future

PREP ARING DATA FOR ITEM  ANALYSIS (Payne,1992) 

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Arrange test scores from highest to lowest. Get one-third of the papers from the highest scores and the other third from lowest scores. Record separately the number of  times each alternative was chosen by the students in both groups.

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Add the number of correct answers to each item made by the combined upper and lower groups. Compute the index of difficulty for each item, following the formula 

IDF = (NRC / TS) X 100)

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Where:

IDF = index of difficulty  NRC = number of students responding correctly to an item  TS = total number of students in the upper and lower groups 

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Compute the index of  discrimination, based on the formula: 

IDN = (CU ± CL) / NSG 

Where:  

IDN = index of discrimination CU = number of correct responses of the upper group CL = number of correct responses of the lower group NSG = number of students per group

DIFFICULTY INDEX OF A TEST ITEM CAN BE INTERPRETED WITH THE USE OF THE FOLLOWING TABLE OF EQUIVALENTS:

RANGE DIFFICULTY INDEX 20 and below very difficult 21 ± 40 difficult 41 ± 60 average 61 ± 80 easy 81 & above very easy

USING INFORMATION ABOUT INDEX OF DISCRIMINATION RANGE .40 & above .30 - .39 .20 - .29 .09 - .19

VERBAL DESCRIPTION very good item good item fair item poor item