Centre 0
12,413 images in total
- Rare-disease training images
- 184
- Share of all rare-disease data
- 47.8%
- Share of FedAvg weight
- 53.4%
- Knowledge vs weight
- 0.90×
01 · The problem
The hospital that knows most about rare diseases gets one of the smaller votes.
Standard federated averaging (FedAvg) weights each hospital by how many images it holds in total, not by what it knows. On the real Fed-ISIC2019 split that shortchanges the one hospital that specialises in the rare diseases.
The gap
Centre 2, in one number.
more of the rare-disease data than its share of the vote.
Rare-disease training images held by Centre 227.0%
Aggregation weight FedAvg gives Centre 214.5%
104 of 385 rare-disease training images · 2,691 of 18,597 training images overall
Every hospital
The same comparison, for all six.
Only Centre 2 holds far more of the rare-disease data than its weight. Centre 4 holds none at all - yet under FedAvg it still votes on rare diseases.
Side by side
Training split. Centre 2 highlighted.
What counts as rare
Two diseases, about one percent each.
A disease is rare here if it holds under 1/25 of the largest class's share (Melanocytic nevus, 48.7%) - a 1.95% cutoff. The rule was chosen after seeing the counts, and we say so.
Rare
Dermatofibroma
1.03%
of all images
4 of 6
hospitals hold ≥ 20 training images
Rare
Vascular lesion
1.09%
of all images
3 of 6
hospitals hold ≥ 20 training images
Who can check
Few hospitals can vouch for a rare disease.
Counting hospitals with at least 20 training images of each disease. If one of only three holders misreports, there may be nobody left to contradict it - and it isn't only the rare diseases that are thinly held.
| Disease | Share of data | Hospitals holding it |
|---|---|---|
| Melanoma | 18.00% | 6 of 6 |
| Melanocytic nevus | 48.72% | 6 of 6 |
| Basal cell carcinoma | 14.29% | 3 of 6 |
| Actinic keratosis | 3.73% | 3 of 6 |
| Benign keratosis | 10.44% | 5 of 6 |
| DermatofibromaRare | 1.03% | 4 of 6 |
| Vascular lesionRare | 1.09% | 3 of 6 |
| Squamous cell carcinoma | 2.70% | 2 of 6 |