American households are allocating so much money to U.S. stocks that the valuation of the whole market is now dependent on their appetite, according to JPMorgan.

Individual investors have become the most important holder of U.S. equities, owning around 60% of the universe, the Wall Street firm said. This record level of ownership creates a lockstep movement between the price-to-earnings ratio of the S&P 500 and the retail flow into the market.