Glossary of Statistical Terms

Score Data Number of Graded Items Displays the number of items on the test that were graded.
Total Points Possible Displays the total number of points on the test.
Maximum Score Displays the highest score from the graded tests.
Minimum Score Displays the lowest score from the graded tests.
Statistics Mean Score Displays the average score of all of the graded tests.
Mean Percent Score Displays the average percent score of all of the graded tests.
Benchmark Score Displays the benchmark percent score entered in Advanced Grade, if applicable. This is the score you want your students to achieve to be considered proficient. You may compare it to the Mean Percent Score to see how students are measuring up to the benchmark.
Range of Scores The range is the distance between the highest and lowest score.
Standard Deviation A measure of the dispersion of a set of data from its mean. The more spread apart the data is, the higher the deviation. It is calculated by taking the square root of the variance.
Variance The amount that each score deviates from the mean squared (by multiplying it by itself).
Achievement Gap Displays the difference between the student's score and the mean (average) score for the question, as well as a bar chart showing the relationship between the mean score and the student's score.  The vertical blue line depicts the mean score.  If students' bar charts are green, they have scored higher than the mean.  If students' bar charts are red, they have scored lower than the mean.
Percentiles Percentile
(25 and 75)
Percentiles are values that divide a sample of data into one hundred groups containing (as far as possible) equal numbers of observations. For example, 25% of the data values lie below the 25th percentile
Median Score The median of the scores from the graded tests.
Inter Quartile Range The difference between the 75th percentile and the 25th percentile
Confidence Intervals Confidence Interval
(1, 5, 95 and 99%)
A confidence interval gives an estimated range of values that is likely to include an unknown population parameter, the estimated range being calculated from a given set of sample data. If independent samples are taken repeatedly from the same population, and a confidence interval calculated for each sample, then a certain percentage (confidence level) of the intervals includes the unknown population parameter. Remark Classic OMR calculates Confidence Intervals of 1%, 5%, 95% and 99%.
Test Reliability Kuder-Richardson Formula 20 This formula measures test reliability and is an overall measure of internal consistency. A higher value indicates a stronger relationship between items on the test.
Kuder-Richardson Formula 21 This formula measures test reliability and is an overall measure of internal consistency. A higher value indicates a stronger relationship between items on the test.
Coefficient (Cronbach) Alpha A coefficient that describes how well a group of items focuses on a single idea or construct.
Standard Error of Measurement The standard deviation of errors of measurement that are associated with test scores from a particular group of students. When used to calculate confidence bands around obtained test scores, it can be helpful in expressing the unreliability of individual test scores in an understandable way. Score bands can also be used to interpret intraindividual and interindividual score differences.
Point Biserial A measurement of the discrimination of an item.  It indicates the relationship between a response for a given item and the overall test score of the respondent.  The point biserial tells you if a question was a good discriminator between the better students and the poorer students.  Point biserial ranges from -1 to 1.  A positive value indicates that the students who did well on the test answered the question correctly.