Enter Survey Inputs
This form uses six rating classes. Adjust scores, counts, thresholds, and reporting precision to suit your survey design.
Example Data Table
This example matches the default form values and demonstrates how weighted ratings produce a severity index.
| Class | Score | Count | Score × Count |
|---|---|---|---|
| Class 0 | 0 | 18 | 0 |
| Class 1 | 1 | 14 | 14 |
| Class 2 | 2 | 10 | 20 |
| Class 3 | 3 | 6 | 18 |
| Class 4 | 4 | 4 | 16 |
| Class 5 | 5 | 2 | 10 |
| Totals | 54 | 78 | |
Example result: DSI = (78 ÷ (54 × 5)) × 100 = 28.89%, incidence = 66.67%, mean rating = 1.44.
Formula Used
Disease Severity Index (%)
DSI = [Σ(ri × ni) ÷ (N × Rmax)] × 100
Mean Rating
Mean = Σ(ri × ni) ÷ N
Incidence (%)
Incidence = (Number of units with score above 0 ÷ N) × 100
Conditional Severity (%)
Conditional Severity = [Σ(ri × ni) ÷ (I × Rmax)] × 100
Variance
Variance = Σ[ni × (ri − Mean)2] ÷ (N − 1)
Estimated Yield Loss (%)
Estimated Yield Loss = DSI × Yield Loss Factor ÷ 100
Where ri is the class score, ni is the class count, N is total assessed units, I is infected units, and Rmax is the highest rating score.
How to Use This Calculator
- Enter a study name, assessor, location, and survey date.
- Set the action threshold and optional yield loss factor.
- Choose the confidence level and decimal precision.
- Adjust the class scores if your rating scale differs.
- Enter the observed counts for each severity class.
- Submit the form to generate DSI, incidence, variation, and threshold status.
- Review the class detail table and Plotly graph for distribution patterns.
- Use the CSV or PDF buttons to export the current report.
Frequently Asked Questions
1) What does the disease severity index measure?
It measures weighted disease intensity across all assessed units. Unlike simple incidence, it captures both how many units are affected and how severe the observed symptoms are.
2) How is DSI different from incidence?
Incidence counts presence versus absence of disease. DSI adds rating intensity, so two fields with equal incidence can still show very different severity levels.
3) Can I use a custom scoring scale?
Yes. You can edit all six class scores. This is useful when your survey uses percentages, ordinal scores, or a site-specific severity rubric.
4) Why is the highest class score important?
The highest score normalizes the weighted total. Without that maximum, the index cannot be converted into a comparable percentage scale.
5) What is conditional severity?
Conditional severity measures average severity among infected units only. It helps separate symptom intensity from simple infection spread.
6) Why include variance and standard deviation?
They describe rating dispersion. Higher spread means symptoms are less uniform, which can matter when comparing plots, treatments, or survey dates.
7) What does the threshold status tell me?
It compares the calculated DSI with your action threshold. This helps flag whether treatment, inspection escalation, or closer monitoring may be justified.
8) When should I export the report?
Export after checking scores, counts, and thresholds. The CSV is useful for spreadsheets, while the PDF works well for formal reporting and documentation.