Bond market investors are showing the greatest confidence in global economic growth since credit markets crashed three years ago. Yields on debt securities are rising for a fourth month as prices fall, the longest stretch since June 2008, according to Bank of America Merrill Lynch’s Global Broad Market Index, which tracks the performance of more than 19,000 securities valued at about $39 trillion. While the highest-rated debt, from U.S. Treasuries to Microsoft Corp. debentures, are falling, the riskiest company notes are returning the most in eight years. “We’ve just experienced the first several months of a bear market in bonds,” said Michael Hyman, head of investment-grade credit in Atlanta at ING Investment Management, which oversees about $518 billion.