Is there a good common practice of saying that RMSE (or whatever model parameter) are "stable" across the three sets. Is there any rule of thumb stuff? Within 10% of each other, etc?

Currently I'm just taking another RMSE vs the mean for the points, but don't know if that would be a valid metric or if there's already somethign out there that accomplishes this. This assumes the same dataset.

```
Names default to here(1);
//Training, Validation, Testing Respectively
RMSE1 = [12.23434, 15.1546, 10.6572];
RMSE2 = [12.23434, 12.526, 12.0000];
RMSE3 = [12.23434, 12.23434, 12.23434];
stable1 = sqrt(mean((mean(RMSE1)-RMSE1)^2));
stable2 = sqrt(mean((mean(RMSE2)-RMSE2)^2));
stable3 = sqrt(mean((mean(RMSE3)-RMSE3)^2));
show(stable1, stable2, stable3);
```

What I'm eventually trying to do is pick a model that has "Good" stability and a low RMSE. I feel like this has to be a common thing, but I can't find good practices.