204 As what / than what in comparative clauses

A - feature is pervasive or obligatory9
B - feature is neither pervasive nor extremely rare25
C - feature exists, but is extremely rare16
D - attested absence of feature18
X - feature is not applicable (given the structural make-up of the variety/P/C)2
? - no information on feature is available7

Feature area:
Typical example:
Itʼs harder than what you think it is.
Example source:
Kortmann/Szmrecsanyi (2004)
Variety World Region Type Value
Id Primary text Variety Variety Type