When developmentalists have considered fluid and crystallized intelligence to determine if intelligence continues to grow, slow, or decline with age, they determined that

The answer is closed primary.

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.