After months of sitting on the investing sidelines while US markets and the economy registered sustained, record-breaking growth, sentiment among wealthy investors hugely increased in August, according to Spectrem Group.

Both the Spectrem Affluent Investor Confidence Index (SAICI) and Spectrem Millionaire Investor Confidence Index (SMICI) improved from July. The SMICI, which measures changes in investment sentiment among investors with $1 million or more in investable assets, rose from eight in July to 20 in August, marking the largest one-month increase since January 2014. For the first time since April of 2017, and only the fourt...