I took your explanation to mean: Cancer is common, so the genetic blueprint for Cancer risk factors should also be common. We have a higher number of samples to verify against which increases the detection accuracy.
For less common diseases, we have a smaller pool to verify against, so our blueprint is less accurate. Lower detection accuracy.
How is error rate being defined in this case?
I took your explanation to mean: Cancer is common, so the genetic blueprint for Cancer risk factors should also be common. We have a higher number of samples to verify against which increases the detection accuracy.
For less common diseases, we have a smaller pool to verify against, so our blueprint is less accurate. Lower detection accuracy.