# education.attendance-rate

A pupil's attendance and absence rates in basis points (9000 is 90.00%), and
whether they are persistently or severely absent under the Department for
Education's definitions for schools in England.

## The definitions, and why they are data

- **Persistent absence**: missing 10% or more of the pupil's own possible
  sessions. This is the definition from the 2015/16 academic year. It was
  introduced in 2005/06 at 20%, and from 2010/11 was about 15% measured
  against a standard number of sessions rather than the pupil's own, which
  cannot be expressed as a percentage of one pupil's sessions; a date before
  1 September 2015 is therefore refused rather than answered with today's
  rule.
- **Severe absence**: missing 50% or more. The data carries it from the
  2018/19 academic year, the first year for which the DfE statistics release
  reports it; before 1 September 2018 `severelyAbsent` is null.

Both are dated rows in `data/absence-thresholds.json`, and `onDate` picks
the row in force.

## Decisions

- **The flags use the exact fraction.** A pupil who missed 250 of 2,501
  sessions has an absence rate of 9.996%, which rounds to 1000 basis points,
  but is not persistently absent: 250 is less than 10% of 2,501. Comparing the
  rounded rate is the naive mistake; a vector pins it.
- **Absence is rounded, attendance is derived.** Absence is rounded half-up
  to a basis point and attendance is 10000 minus that, so the two always add
  up to 100%. (Rounding both half-up gives 10001 when each sits on a half.)
- Sessions are whatever the school counts: two per day (morning and
  afternoon) in England. Missed sessions include authorised and unauthorised
  absence, as the DfE measures do; pass only the sessions you want counted.
- No possible sessions is an error: there is no rate to report.

## Sources

- Department for Education, "Pupil absence statistics: methodology"
  (Explore education statistics): definitions of persistent absence (10% or
  more of a pupil's own possible sessions, from 2015/16) and severe absence
  (50% or more), and the history of the persistent absence threshold:
  https://explore-education-statistics.service.gov.uk/methodology/pupil-absence-statistics-methodology
- Department for Education, "Pupil absence in schools in England: 2018/19",
  the first release reporting severe absence:
  https://explore-education-statistics.service.gov.uk/find-statistics/pupil-absence-in-schools-in-england/2018-19