Missing is not zero¶
Eye-tracking pipelines frequently create quantities that look numeric but have different observation states.
Distinguish the states¶
Observed zero means the quantity was observable and its measured value was zero.
Missing means the value was expected but unavailable.
Absent by design means the quantity was not part of that observation's design or exposure.
Undefined means the mathematical quantity cannot be computed for that row.
Right-censored latency means the event was not observed before the observation window ended; it does not mean latency was zero.
Why zero-filling is dangerous¶
Replacing these states with zero changes means, proportions, rates, event counts, exposure-adjusted summaries, and model likelihoods.
Carry observation state into the handoff¶
Statistical analysis should receive the measurement, denominator or exposure, grouping identity, and missing/censoring state together.