The traditional 4% withdrawal rule used by retirement planners is a "risky strategy" in today's low-yield environment, a study co-author says. The early years of retirement have a "disproportionate impact on failure rates," which could reach 57% based on 2013 yields, researcher Michael Finke says. Advisers should "start with having a more conservative approach to estimating retirement income," says Finke, who suggests that annuities can offer some protection.