Crime analysis units often face personnel shortages that can be alleviated somewhat by employing volunteers. Police training is needed so that officers can fully understand the function of a crime analysis unit, whose central position in the police department structure is necessary to facilitate information flow to users in all other units. Formal quality control procedures are needed within a police department so that police offense reports contain information pertinent for crime analysis. Liaison/communication between crime analysis units located at both headquarters and precinct levels is required, since such units share information. Crime analysis units can assist patrol officers by coordinating cases, identifying similar crime patterns and methods of operations, and identifying high crime areas/targets. There are nine types of crime patterns, including geographic, sequence, combination, seasonal/yearly, duplicate, and similar offense patterns. Before crime trends can be compared, norms should be established for an area and comparisons kept consistent. Under the directed patrol system police sergeants are given the burden of using their uncommitted time (time not spent on calls-for-service), and management is encouraged to create an environment conducive to the sergeants' effective functioning. Call prioritization, the involvement of district officers in planning, and a manpower allocation system are other components of the directed patrol system. Police sergeants are also instructed to document their activities (the problem observed, why it is a problem, and what the sergeants expect to be done about it).