Performance by Subgroup: The Sum of the Parts Is Greater than the Whole. Research Brief. Volume 1302

When comparing overall FCAT performance of the District to the State, the Miami-Dade County Public Schools District comes up a little short in Reading and barely higher in Math. However, when the comparisons to the State are confined within the typical subgroup categories, the District meets or exceeds the State's performance in all subgroups. This reversal in trend between the whole and the parts seems to defy common sense. How is it possible that the district appears better than the State in all subcategories but worse overall? This research brief attempts to explain how the incongruity between overall and part comparisons can take place and underlines the importance of considering subgroup breakdowns when assessing district performance.