Description
Calculate overlap duration of supplied risk and observation intervals.
Statistical record calculations depend on risk-set boundaries, cluster assumptions, missingness codes and exposure definitions. Entry can be excluded while exit inclusion is a policy choice, and one design-effect formula assumes equal cluster sizes. A local flag or contribution does not fit a model or establish a clinical result.
Calculate overlap duration of supplied risk and observation intervals.
When to use this tool
Use Person Time Interval At Risk when you already have entryTime, exitTime, observationStart, observationEnd and need to calculate overlap duration of supplied risk and observation intervals.
How to use the tool and how it works
- Enter entryTime, exitTime, observationStart, observationEnd. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read atRiskTime. Use the output convention below.
Require both intervals ordered; return max(0,min(ends)-max(starts)).1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| entryTime | Entry Time | Required. Finite number. |
| exitTime | Exit Time | Required. Finite number. |
| observationStart | Observation Start | Required. Finite number. |
| observationEnd | Observation End | Required. Finite number. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| atRiskTime | Positive overlap width of the supplied observation and risk intervals; touching boundaries give zero. | Required. Finite number. |
{
"input": {
"entryTime": 2,
"exitTime": 10,
"observationStart": 0,
"observationEnd": 8
},
"output": {
"atRiskTime": 6
}
}Limitations and assumptions
- Touching endpoints have zero duration. This is continuous overlap, not inclusive calendar dates, an estimated survival probability or verified person-time.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use the complete study design, data and statistical model for inference. Check censoring, clustering, visit windows, exposure and missingness conventions before combining these terms, and assess uncertainty with the full analysis.
References
Similar or alternative tools
- Risk Set Event Inclusion Check
Check supplied event-time membership in an entry-exclusive risk interval.
- Contribution Person Days Exclusion Offset
Subtract supplied excluded person-days from recorded exposure.