Yahoo Finance, citing JPMorgan Chase research since 1970, found that investing when the S&P 500 hits an all-time high yields an average return of 9.4% over the next 12 months, slightly higher than the 9% when it's not at a new high. If the measurement period is extended to two years, the difference in returns becomes even more significant, at 20.2% versus 18.5%. The article suggests that despite current high valuations in U.S. equities, historical experience indicates that a market at elevated levels should not be a reason for investors to avoid long-term investments.