Page 310 - DEDU504_EDUCATIONAL_MEASUREMENT_AND_EVALUATION_ENGLISH

Educational Measurement and Evaluation

Notes When the value found out using these methods is 10 or more, the discriminating power
of the item is considered satisfactory. The items with less than this discriminating power
are not considered suitable for the test. If the value of DP comes in negative, the item is
considered very poor.
Example
The analysis of obtained marks in an achievement test for item number 23 is as follows.
Find out the discriminating power of the item.
Class Number of Students Correct Solution Unattempted

High 54 40 10
Low 54 25 5

Solution
R = 40, R = 25, N = 54,
H
L
H
N = 54, NR = 10, NR = 5
L
H
L
Here the value of R is more than R , so the first formula will be used.
H
L
N = N + N = 54 + 54 = 108
T H
R = R + R = 40 + 25 = 65
T H L
NR = NR + NR = 10 + 5 = 15
T H L
R– R – 1
So, DP = ⎛ H L ⎞
R T ⎜ R T ⎟ 1 –
⎝ N– NR T ⎠
T

40 – 25 – 1
= 65
65 ⎛ ⎜ ⎞ ⎟ 1 –
⎝ 108 – 15 ⎠

14
=
⎛ ⎞ 28
⎜ 65 ⎟
⎝ ⎠ 93

14
= 1820
93

14 14
= = = 3.17
19.5698 4.42
So, the discriminating power = 3.17
Note :
The following formulae are used to know the difficulty level and discriminating power
of the teacher-made tests respectively :

R + R
DL = H L
2N

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