Symbol concentration
How much of an account's result comes from a single traded instrument.
A signal history can list many symbols while almost all of its net profit comes from one of them. In that case the record is really evidence about that one symbol, with the sample size of that one symbol, whatever the total trade count says.
The other symbols traded add rows to the history without adding independent evidence that the strategy works, which is why a verdict weighs the share of profit per symbol, not just the count of symbols traded.