Madison leaders and economists are still working to predict all of the major changes that could take place with the sale of local cancer diagnostics company Exact Sciences to Illinois-based Abbott Laboratories, which was announced late last month. But one local economist and business analyst says the merger is likely to be a net positive for both companies. Dan Olszewski, director of the Weinert Center for Entrepreneurship at the University of Wisconsin-Madison School of Business, studies mergers and acquisitions in prominent companies.