With companies like WPP Group and newer digital start-ups encroaching on its audience-research business, Nielsen has to find ways keep growing. Small purchases are one way to do that. The Nielsen Company announced today that is buying The Cambridge Group, a consulting firm based in Chicago. The Cambridge Group helps Fortune 500 companies with growth strategies. Still for Nielsen, buying the consultancy seems more like a way to hold on to its larger clients than trying to attract new ones. Also, buying service-oriented companies can be tricky because in most cases the value of the company is in its employees, many of which tend to leave shortly after the deal closes.

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