Tom Davenport of Accenture and Larry Prusak of IBM believe that 70 to 80 percent of learning is done through informal means. This implies that a personalized approach as opposed to a codified approach to knowledge management and building a learning organization should be a critical part of an organization's human capital strategy. Rob Cross of the University of Virginia and Larry Prusak, in their article "The People Who Make Organizations Go—or Stop" (Harvard Business Review, June 2002), present evidence that the real work in organizations is done informally, through personal contacts. Their research indicates that the executives can manage and enhance the effectiveness of these informal networks by focusing their attention on the key role-players in the group. Cross and Prusak feel that there are four common role-players: central connectors, boundary spanners, information brokers, and peripheral specialists. The central connectors link most people in an informal network with one another. Boundary spanners connect an informal network with other parts of the company or with similar networks in other organizations. Information brokers keep the various subgroups in an informal network together. Peripheral specialists are people in an informal network that others can turn to for specialized expertise. Cross and Prusak further believe that it is only after executives openly and systematically start working with informal networks that the groups will become more effective.