When, pursuant to RCW 43.20A.400 through 43.20A.430, the secretary elects to purchase a service or services, he or she shall retain continuing basic responsibility for:
(1) Determining the eligibility of individuals for services;
(2) The selection, quality, effectiveness, and execution of a plan or program of services suited to the need of an individual or of a group of individuals; and
(3) Measuring the cost-effectiveness of purchase of services.