No bull market can last forever. The US equity surge is now in its seventh year, making it the longest bull run since World War II uninterrupted by a fall of more than 20 percent. Fears mounted through 2015 that the post-crisis upswing in risk assets is finally running out of steam. Confidence was shaken in August and September by worries over China's growth, despite the fact that, at least according to official data, growth is meeting expectations.

With that in mind, we see six key questions for investors in 2016: