5 CFR 831.905: Evidence.

(a) An agency head's determination that a position is a primary position must be based solely on the official position description of the position in question, and any other official description of duties and qualifications. The official documentation for the position must establish that it satisfies the requirements defined in § 831.902.

(b) A determination under § 831.904 must be based on the official position description and any other evidence deemed appropriate by the agency head for making the determination.