Sorry
That's Incorrect

No. Because there is only one participant, the
external validity of single-subject designs is poor.
With a single participant, we cannot adequately sample
from a large population so that our sample represents
that population and the variation of characteristics within it.
It is for this reason that one of the major uses of
single-subject designs is in clinical research, where the
outcomes concerning single, specific individuals,
are the most important findings.