The name Katie ranked 103rd in popularity for females of all ages in a sample of 2000-2003 Social Security Administration statistics, 193rd in popularity for females of all ages in a sample of the 1990 US Census and 59th in popularity for females of all ages in a sample of the 1994 US Census.
This name was popular earlier in the 20th century, then fell off in usage, but has begun making a comeback in recent years.
This meaning assumes the source name was derived from the Greek term katharos. However, it may have evolved from Hecate, the name of the Greek goddess of magic. Another possible source is katateinô, the Greek word for torture.
All three meanings might have been associated with St. Aikaterine (Katherine) of Alexandria, who was born a pagan but died as a Christian martyr.