Longer relationships can allow a staffing firm to know more about its workers. A firm can then use that knowledge to make better placements -- and charge higher initial rates for the placements, according to the study.

The research was done by Isabel Fernandez-Mateo, assistant professor of strategic and international management at London Business School, and Matthew Bidwell, assistant professor of management at the Wharton School in Pennsylvania. The research was based on a large U.S. staffing firm that placed skilled, creative information technology professionals such as graphic and Web designers.

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