The following are descriptions of some of the most frequently asked about
metrics generated by the ParScore Item Analysis Report.
Reliability Coefficient (KR20) – this is the correlation coefficient between two sets of test
scores. A coefficient value of 0 indicates that there is no relationship between the two sets of
test scores. A coefficient value of 1 would be indicative of the same score occurring on both
administrations of the test. In essence, the higher the score, the higher the reliability.
The range of the reliability coefficient (KR20) can be interpreted as follows:
Range
Interpretation
.90 or Greater
High Reliability
.80 to .89
Good Reliability
.60 to .79
Low to Moderate Reliability
.40 to .59
Doubtful Reliability
Total Group – this is the percentage of total students who responded correctly to the test
question.
Upper 27% of Group – Of the upper 27% of the test takers, this is the percentage that
answered a given question correctly.
Lower 27% of Group – Of the lower 27% of the test takers, this is the percentage that answered
a given question correctly.
Discrimination Index – this measures the effectiveness of a question, as a whole, by
discriminating between those who have and have not mastered the material.
The range of the discrimination index can be interpreted as follows:
Range
Interpretation
0.40 to 1.00
Excellent Question
0.25 to 0.39
Good Question
0.00 to 0.24
Room for Improvement
Less than 0.00
Unacceptable
Distracter Analysis – this is an analysis of the incorrect response options for a given test
question and provides the percent of students who selected a particular distracter or incorrect
response.
Point Biserial (Pt-Biser) – this metric, ranging from -1 to 1, is presented within the Distracter
Analysis section of the report and measures the correlation between an individual response
option for a question and the total test score of a student. In essence, it details how well an
item predicts student performance on the entire test by comparing how well students did
answering one question with how well students did answering all of the questions.
The point biserial for incorrect response options will tell you how good of a distracter that
response option is.
Note: The discrimination index will be equal to the point biserial for the correct response option
to a test question.
The range of point biserial coefficients can be interpreted as follows:
Range
Interpretation
.30 or Greater
Very Good Test Distracter
.20 to .29
Reasonably Good Test Distracter
.09 to .19
Needs Improvement
Less than .09
Poor Test Distracter
If the point biserial coefficient is negative or a low positive integer, you may want to examine
the test question for the following:
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An ambiguous question stem
A questionable correct answer
More than one correct answer
No real correct answer