A great deal of research into occupational stress shows that negative work experience is a major cause of stress. Labor process writers have shown that occupational stress is greatest for those in lower occupational groups, and argue that this results from working conditions in which workers lack control over the labor process. Schwalbe and Staples used "lack of control" and "job routine" as important outcomes of the organization of the labor process for the nature of work for lower level employees. Braverman identified the causes of negative and alienating work as structural: he focused his argument about the effects of management control on the labor process on point-of-production activities. The effects of three outcomes of management control were tested: control over task activities, control over structure, and the effects of control on the climate of attitudes and values of management toward workers.