South Korea's national pension operator reduced the portion of top business groups in its stock holdings in 2013, market data showed Sunday, in an apparent move to hedge against the market's volatility by diversifying its portfolio. The National Pension Service (NPS) said shares in the affiliates of South Korea's top four conglomerates -- Samsung, Hyundai Motor, LG and SK -- took up 52.5 percent of its stock investment portfolio at end-December 2013, down 6.5 percentage points from a year earlier.