The board is authorized to grant postretirement benefit adjustments from time to time for the purpose of maintaining essentially no less purchasing power for persons receiving benefits pursuant to the provisions of this chapter. Granting postretirement benefit adjustments shall be based on the following factors:

(1) The recommendations of the actuary for the retirement system;

(2) Maintaining the actuarial soundness of the retirement system;

(3) Appropriations by the General Assembly if appropriations are made for the purpose of granting such postretirement benefit adjustments; and

(4) Such other factors as the board finds relevant.