Item Analysis What makes a question good??? Answer options? Multiple Choice Questions Elements of a good multiple choice question???? Item Analysis How can we determine if it is a good question????? Distractor power Item difficulty Item
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Presentation Transcript
01
Item Analysis What makes a question good???
Answer options?<br>
02
Multiple Choice Questions Elements of a good multiple choice question????<br>
03
Item Analysis How can we determine if it is a good question?????
Distractor power
Item difficulty
Item discrimination<br>
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Distractor power Strength of each distractor (should be equal)
# answering incorrect
# of distractors<br>
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E.G. There are 4 possible answers
Option a is correct
if 9 people choose option b (9/3 = 3)
and 12 people choose option c (12/3 = 4)
and 15 people choose option d (15/3 = 5)
then option d is the strongest distractor<br>
06
Item Difficulty = p (percent of people passing) p = number answering correctly
total number answering
If 100 people take the test and 34 get question 1 correct, what is the difficulty of that question?
p1 = 34/100 = .34
For 65 correct p would be 65/100 = .65
SO… the higher the p, the easier the question
(score must be between 0 and 1)<br>
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Item Difficulty is... A behavioral measure
Based on the current group
Allows internal comparison
Also allows external comparison<br>
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In construct based tests Item difficulty is similar to item endorsement
Number agreeing with an item<br>
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Item endorsement also... A behavioral measure
Based on the current group
Allows internal comparison
Also allows external comparison<br>
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Item discrimination = d Does the question discriminate between those who do well overall and those who do poorly?
(or on a psychological test, those scoring high or low on the construct)<br>
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Distribution To determine level
upper (U) = top 25 to 33 % of scores
lower (L) = bottom 25 to 33 % of scores<br>
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Determining item discrimination d = U-L
n
where d = item discrimination
U = number in the upper group who get question correct
L = number in the lower group who get question correct
n = number in one group (U or L)<br>
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Examples of d With 33 in U and L
if all in U and all in L get it correct
33 - 33 / 33 = 0
if all in U get it correct, and none in L
33 - 0 / 33 = 1
if none in U get it correct, and all in L
0 - 33 / 33 = -1
if 30 in U and 10 in L get it correct
30 - 10 / 33 = .61<br>
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Value of d Range for d = -1 to 1
higher d indicates more discriminating (1 = all in upper group got it correct and none in lower group)
negative d indicates a really bad question (-1 indicates all in lower group got it correct and none in upper group)<br>
