Vanguard's December 2014 economic outlook indicates that global economic growth will remain fragile, with varying cyclical risks across major economies, particularly highlighting the U.S. economy's resilience amidst global challenges. The report warns of persistent deflationary threats and divergent central bank policies, with the Federal Reserve expected to raise rates while other central banks may struggle to do so. Vanguard's projections for global stocks and bonds are cautiously guarded, suggesting that long-term returns will likely be below historical averages and recommending cautious asset allocation strategies.