Effective in 2024-25, the default data display on FastBridge reports has been set to show national norms for all Iowa districts. Previously, these reports defaulted to local norms. This frequently created confusion that resulted in misinterpretation of student data.
Why national norms over local norms?
National Norms and percentiles are typically the best way to make a peer referenced interpretation relative to benchmarks and to make comparisons over time. They are more stable over time because the percentiles are based on a broader national sample of student performance, whereas local percentiles are based solely on the performance of the local students in the current testing window. In addition, benchmarks in FastBridge were developed based on national normative data.
Local percentiles tend to be far more variable, especially when there are fewer than a hundred students in the school. Local percentile ranks describe a student’s performance relative to only their current peers. This means there will always be 20% of the students at or below the local 20th percentile because a percentile score describes how a student’s performance ranks against the local comparison group only. Furthermore, when the local group of students have skewed performance (mostly very high or very low achieving), the resulting percentiles are impossible to interpret meaningfully. What local percentile ranks do provide is the student’s relative performance level when compared to local peers.
At this time, if the reports are set to national norms, local norms are not used anywhere in the system. If a district prefers that reports use local norms at all buildings, please submit a ticket to the Iowa support team for assistance. Be aware it is a district-wide setting that cannot be overridden in most reports.
Interpreting percentile rank scores
A percentile rank score is a way of evaluating a student’s performance in relation to a comparison group. If a student has a percentile rank score of 55, it means they scored higher than 55% of the students in the comparison group. When comparing percentile rank scores over time, if the comparison group remains the same, and the student’s percentile rank decreases, the student is losing ground when compared with the norm group. If the percentile rank increases, they are gaining, or moving up in the ranks. If the student’s percentile rank stays about the same, they are growing at the same rate as the comparison group grew. Think of it as a group of students marching ahead. Does the target student move up in the ranks, stay the same, or move back through the ranks over time? Be careful about over-interpreting small differences, since there is typically a small amount of error in testing over time. Small changes may just be variations in the test due to random error.