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How the operation start time was charted

The charted operation start time is a mixture of 3 ways of writing a clock time (nearest_10min, nearest_5min, clock_minute), modelled as an offset from a device time.
Date 2026-10-18
Status current
Methods Rounding, heaping and value resolution, Clinical and laboratory times
Variables Operation start time

Background

  • Op start is a charted event time with a 1-minute chronon.
  • Op start, op end and anaesthesia end share a 5-minute grid. Op start falls on a 5-minute clock mark in 92% of cases.

Data

  • 6,387 op starts.
  • One op start does not share the sub-minute offset of the other charted times in its case and is flagged clock_offset_mismatch.

Method

  • The same approach as the anaesthesia times: the true op start is placed a log-spline offset after the recording start (K = 10).
  • First cases get a clock-time prior, as for anaesthesia start.
  • Nearest, floor and ceiling anchors were compared. 30- and 60-minute modes and effects of time of day and emergency status were tested.

Results

Bar chart of charted times by minute past the hour, with tall bars on multiples of five.
The minute past the hour of every charted time: the heaps on multiples of 5, and at the standard first-case times, are the rounding modes the model fits.
  • There is no 30- or 60-minute rounding, and no effect of time of day or emergency status.
  • The anchor is nearest (floor is 14 BIC points worse, ceiling 101).
  • First-case incisions cluster at 08:20–08:50; the clock-time prior is 1,120 BIC points better.
  • Unlike anaesthesia start, there is no scheduled or nominal op start time.
  • Op start is well centred: a rounded value is uncertain by ±2.5 min.
  • Since vitaldb-resolution v0.6.0 (18 October; model version 2): the log-likelihood gap is explained. The old fitter worked out the time-of-day prior on its own 0.1-minute grid; refitted with the library's likelihood the model gains 33.2 in log-likelihood and the posteriors move by less than 0.03 minutes.

Discussion

  • Before v0.6.0 the package's log-likelihood differed from the stored one by −10.6. The cause was the fitter integrating the first-case clock prior on its own 0.1-min grid; model version 2 is fitted with the library's likelihood.

Model

Model file: …/models/opstart.model.json. Read from the pinned snapshot of vitaldb-resolution at commit bb03ddfc8a (2026-10-18).

How a true value becomes the recorded one. The rules are tried in order: a record not taken by an earlier rule is taken by this one with the probability shown (where its condition holds); the last rule takes the rest. With no conditions, the shares follow directly.

Order Rule Rounds to Probability if reached Share of records
1 nearest_10min 10 clock minute (nearest) 5.6 % 5.6 %
2 nearest_5min 5 clock minute (nearest) 89.6 % 84.6 %
3 clock_minute 1 clock minute (floor) the rest 9.8 %
Recorded resolution 1 min (chronon) (modelled at 1)
True-value density reference_offset_spline
Covariates ref
Fitted on 6,387 records (clinical_data.csv)
BIC 36,239
Fitted 2026-10-18

Code

Tags: generated, vitaldb-resolution