Disease-Frequency Measures Calculator

Scope

This calculator estimates one population’s disease or health-event frequency from aggregate counts. It does not compare populations, calculate association measures, standardize rates, adjust for covariates, reconstruct person-time from dates, or perform survival analysis.

Formula and inference

Population proportions and risks equal the measure-specific numerator divided by its eligible population denominator and use a two-sided Wilson score confidence interval without continuity correction. Person-time rates equal events divided by accumulated time at risk and use a two-sided exact Garwood Poisson interval shared with the Incidence Rate and Person-Time Analyzer.

Assumptions and limitations

• The numerator belongs to the population represented by the denominator and follows one consistent case definition.
• Population denominators contain only eligible persons; person-time contains only time genuinely at risk.
• Simple Wilson intervals assume independent binomial observations and do not incorporate complex surveys, clustering, denominator estimation, nonresponse, or ascertainment error.
• For a complete census, the Wilson interval is a model-based or superpopulation interval; the observed finite-population percentage itself has no population-sampling error.
• Simple cumulative incidence does not adjust for censoring, competing events, changing cohort membership, or informative loss.
• Exact rate intervals assume a Poisson event count conditional on accurately measured person-time.

Validation

Version 1.0.0 was checked against independent R calculations for Wilson score intervals and exact Garwood Poisson intervals. Cross-tool tests confirm that its proportion and rate calculations remain identical to the corresponding validated EPI01 and EPI02 methods. Automated tests cover every measure, boundary inputs, parsing, scaling, reporting, privacy, and responsive-interface behavior. Version 1.1.0 retains these statistical methods with a harmonized interface. Owner review, native PDF pagination and screen-reader listening checks remain pending. Availability does not constitute regulatory validation.

Privacy

All calculations use aggregate values in browser memory. The app does not transmit, upload, or persist entered counts, labels, person-time, or results. Do not enter identifiable or confidential information.

References

1. Centers for Disease Control and Prevention. Principles of Epidemiology in Public Health Practice. Lesson 3: Measures of Morbidity and Mortality Frequency.
2. Newcombe RG. Two-sided confidence intervals for the single proportion: comparison of seven methods. Statistics in Medicine. 1998;17:857–872.
3. Brown LD, Cai TT, DasGupta A. Interval estimation for a binomial proportion. Statistical Science. 2001;16:101–133.
4. Garwood F. Fiducial limits for the Poisson distribution. Biometrika. 1936;28:437–442.
5. R Core Team. stats::poisson.test: Exact Poisson tests.