Certainty
Substrate's separate read on how confident to be in a graded claim. High certainty means the trials converge and the design is robust; low certainty means the point estimate exists but is fragile — small trials, wide confidence intervals, or heterogeneity across studies. Grade and certainty are independent axes: a Grade A claim can still be low-certainty (many trials, none conclusive), and a Grade C claim can be high-certainty (few trials, but they agree tightly).