Definition
Total Time on Test (TTT) is the cumulative operating time contributed by all subjects in a survival study until the last failure or censoring time:
where is the failure or censoring time for subject .
Interpretation
TTT represents the total “machine-hours” or “person-years” that subjects contributed to the study. It accumulates all observed time, whether the subject experienced the event or was censored.
Applications
| Application | Description |
|---|---|
| Nelson-Aalen variance | Appears in variance calculation for |
| TTT Plot | Diagnostic tool to check if data follows Weibull distribution |
| TTT Transform | Used to assess hazard rate behavior |