In principle, it is reasonable to consider program strength in specific fields and even subfields. The main problems of doing so are two: (1) the candidate may just have a "leaning" toward some field(s) -- not really a well-defined research idea --, and this may change as s/he becomes aware of new material during the 1st/2nd year of the PhD (2) Even if the candidate has a strong field preference and some concrete ideas, s/he still need to *predict* ...