Why Would Outcomes Research Use an Entire Database, Rather Than

Why would outcomes research use an entire database, rather than merely selecting a sample?

A) Use of the whole database provides an analysis that addresses the entire patient population.
B) Permission to use an entire database implies that the entire database must be studied.
C) Small effect sizes and multiple variables demand huge samples, if statistical significance is to be achieved.
D) Periodic review of the entire database makes it possible for the researcher to identify patterns related to outcomes that might be missed if only part of the database were used.
E) Cost is not an issue.