Is There a Difference Between the Concurrent Control and the External Control?

There's no such thing as a definite index date that is similar to when the patient was randomized and dosed, because that's never that kind of nebulus all the time. And if it requires a lot of clinical judgment, when is the index time really defined? Am? We can't, we get into a lot of problems like this, for example, immortal bias,. where at that particularinal period this patient will never experience a particular ani ort.