A<unk>  or<unk>  (British English) is a narrow field of professional knowledge/skills within a specialty of trade, and is most commonly used to describe the increasingly more diverse medical specialties. A subspecialist is a specialist of a<unk> . In medicine, subspecialization is particularly common in internal medicine, cardiology, neurology and pathology, and has grown as medical practice has: # become more complex, and # it has become clear that a physician's case volume is negatively associated with their complication rate; that is, complications tend to decrease as the volume of cases per physician goes up.
Subspecialty
Risk factor
Strain 
Regimen
Drug class
Disease cluster
Residency 
Dose 