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Appendix A: Methodology and Technical Notes

The Common Core of Data (CCD) is a subset of the data collected through the U.S. Department of Education’s EDFacts collection system. State education agencies (SEAs) annually submit over 100 data files through the EDFacts Submission System (ESS). The CCD universe files are based on the data provided in nine of those files. Submission due dates for these files ranged from January 1, 2016, through January 17, 2017. Not all states were able to meet the initial due dates.

ESS checks submitted files for format and conducts some validation checks. Files that pass these initial checks are then passed to the National Center for Education Statistics (NCES) for additional processing.

The school year (SY) 2015–16 collection was the first CCD collection processed completely through EDFacts’ Partner Support Center (PSC) and the new Data Management System (DMS). The PSC used the DMS to reach out to SEAs and resolve any data issues. When errors in data were found, SEAs were encouraged to resubmit the data file through ESS. This provisional release of the CCD universe files is based on the submissions and resubmissions received through January 17, 2017, and is designated as “1a” in file names. Re-releases of these data files will be designated with an incremented release number (e.g., “2a”).

Prior to SY 2014–15, geographic data were included with the CCD directory files. Those data are now processed and published separately by NCES’s Education Demographic and Geographic Estimates (EDGE) program (see for more details).

When SEAs could not resubmit files to correct data problems, NCES made the corrections to the data directly. NCES’s preference is to publish the data as reported by the SEAs. However, NCES makes some adjustments to the reported data for the following reasons:

  • To set appropriate default values.
  • To bring SEAs’ definitions into conformity with NCES definitions (e.g., school types).
  • To carry over corrected data researched and resolved in prior years.
  • To impute for missing values in state-level data.
  • To suppress local education agency (LEA) or school-level enrollment or staff counts that are greatly inconsistent with prior year reports. This suppression is done only if the SEA did not provide an explanation for the anomaly.
  • To suppress high or low counts that might compromise confidential data.

Imputations for missing data are only done for state-level data.

In prior years, NCES has imputed all state-level missing values. In the 2015–16 collection there were number of cases (13 distinct values in 7 states) where the same values in the same states had been imputed by the same method for three or more years in a row. NCES decided to leave these values as missing rather than impute for a fourth year in a row.

More detailed explanations of the methodology used to collect these data and a glossary of CCD terms are available in the Documentation to the 2015–16 Common Core of Data (CCD) Universe Files (NCES 2017–074), available online at