Scale Scores and Error Band

Results from the summative and interim assessments include scale scores as well as an error band (for groups).

Student-Level Information

Each student who completes an interim or summative assessment receives an overall scale score. The scale score is the basic unit of reporting. It places a student’s results along a common score range for an assessment, allowing educators to see where a student’s performance falls within a broader continuum of achievement.

Scale scores can be used to

• describe a student’s overall performance on an assessment,
• compare performance across grade levels or over time, and
• summarize results for groups of students to identify patterns or trends.

Error Band

Assessments provide the most precise scores possible, but no assessment can be 100 percent accurate. Each test score reflects a combination of both student skill and factors unrelated to that skill. Unrelated factors can include the sample of items included on the assessment, the student’s mental or emotional state on the testing day, the student’s luck in choosing more correct answers than incorrect answers when guessing, the conditions under which the student took the assessment, and many others.

Each time a student takes an assessment a scale score and the standard error of measurement (SEM) is calculated for the student’s score. The SEM is an evaluation of the degree to which a student’s test score is expected to change across administrations of parallel test forms because of unrelated factors. The SEM is useful in describing a range for which a student’s actual level of skill is likely. The SEM is accounted for in the student test results by the error bands. The error band indicates a statistical range of scores that the student would likely achieve if they were to take the assessment multiple times. This range represents one SEM above and below the student’s scale score.

For more examples on measurement error, refer to the Tests Results are Not Perfect Measures of Student Performance subsection.

Group-Level Information

Average Scale Scores and Standard Error of the Mean

For group-level reports, an average scale score and error band based on the standard error of the mean for that score are displayed. The average scale score is an average of the scale scores for each individual student in the group. The average scale score is not assigned to an associated achievement level. Instead, a student score distribution displays the percentage of students who performed at each achievement level. The standard error is a statistical term that measures the accuracy with which a sample distribution represents a population by using standard deviation. In statistics, the average mean deviates from the actual mean of the population—this deviation is called the standard error of the mean.