As Wall Street wraps up its flattest year since 2011, investors will have to deal with many of the same issues next year as they attempt to gauge market direction. While many market participants have a host of worries heading into 2016 that could hurt stocks and keep volatility high, they remain optimistic for gains in 2016 and a strong start to the year could boost that case. Stocks could get a boost next week from the so-called “January effect,” when stocks that were sold off in December for year-end tax harvesting rally back in the next month as investors scoop them back up at lower prices.