Retail investors’ appetite for U.S. stocks has fallen in the past week, data from Vanda Research showed on Wednesday, increasing the odds for a broader sell-off in the S&P 500 at a time when it is already about 2 percent off its record high. In the five days to Tuesday, retail investors bought $657.7 million in U.S. equity exchange-traded funds, compared with $989.6 million and $1.39 billion in the preceding two weeks, partly due to a surge in demand for cryptocurrencies, analysts at Vanda wrote in a client note. “Retail investors have bought every minor dip in equities this year, shielding the S&P against a double-digit sell-off (but) this diminishing appetite to support the equity rally raises the odds of a larger sell-off if institutional investors continue to sell,” said Ben Onatibia, senior strategist at Vanda. The benchmark S&P 500 is down about 1.8 percent so far this month on …