Horsfall-Barratt Severity and AUDPC Calculator
Convert Horsfall-Barratt rating-class scores to disease severity percent and integrate AUDPC online for free.
When to use it
Use to convert Horsfall-Barratt 12-class disease ratings to the corresponding mid-class severity percentages, then integrate disease progress over time as Area Under the Disease Progress Curve (AUDPC). Standard plant pathology assessment tool for foliar disease epidemiology.
When NOT to use it
Do not use direct percent ratings as if they were Horsfall-Barratt class ratings; the conversion is not the identity. Do not compute AUDPC from a single time point; you need at least two assessment dates. Do not compare AUDPC across studies with different assessment intervals without normalising.
What you get
Per-treatment per-time-point class-to-percent conversion using the Horsfall-Barratt midpoint formula (Horsfall and Barratt 1945); per-treatment mean severity over time; AUDPC computed by trapezoidal integration; standardised AUDPC (AUDPS / total period); summary table ranking treatments by AUDPC.
Worked example
Two cultivars (susceptible vs resistant) scored on the Horsfall-Barratt 0-11 scale at 7, 14, 21, 28 days post inoculation.
Susceptible: 7=3, 14=5, 21=7, 28=9 Resistant: 7=1, 14=2, 21=3, 28=4
Expected output: Susceptible AUDPC about 4x Resistant AUDPC; final-day severity 75% vs 12% on the mid-class HB conversion.
Source: StatVeda built-in example, paired with the analyse page sample for toolId 'horsfallbarratt'.
How to interpret the output
Lower AUDPC means less disease pressure across the season. Compare treatments by AUDPC rank rather than by single-time-point severity, which can be misleading depending on assessment timing. Standardised AUDPC adjusts for unequal assessment intervals across studies (Simko and Piepho 2012).
Common pitfalls
- Using the class number directly instead of the corresponding mid-class percent.
- Comparing AUDPC across studies without standardising for total assessment period.
- Skipping early or late assessments and biasing the AUDPC integral.
Try it in StatVeda
The Horsfall-Barratt Disease Severity + AUDPC engine runs entirely in the browser. No signup, no install, no data sent to a server. Paste your data, hit Run, copy the output.
Open Horsfall-Barratt Disease Severity + AUDPCReferences
- Horsfall, J. G. and Barratt, R. W. (1945). An improved grading system for measuring plant diseases. Phytopathology, 35, 655.
- Shaner, G. and Finney, R. E. (1977). The effect of nitrogen fertilization on the expression of slow-mildewing resistance in Knox wheat. Phytopathology, 67(8), 1051 to 1056.
- Simko, I. and Piepho, H.-P. (2012). The area under the disease progress stairs (AUDPS): calculation, advantage, and application. Phytopathology, 102(4), 381 to 389.