The buybacks have continued, but companies doing them have trailed the S&P 500 stock index as investors anticipate higher interest rates. Headed into 2016, with the Federal Reserve beginning what many expect will be a prolonged, if slow, cycle of interest rate increases, analysts say the quality of a company’s balance sheet could matter as much as whether it is reducing the number of shares on issue. The Fed is expected to raise interest rates at the end of its Dec. 15-16 meeting for the first time in nearly a decade.