A comprehensive global study by Deutsche Bank, analysing over 200 years of equity market data, reinforces the case for holding diversified stock portfolios over long investment horizons. The report, covering 56 countries and spanning multiple market cycles, finds that stocks have rarely underperformed cash or bonds when held for at least 25 years, despite intermittent periods of volatility.
According to the results, nominal stock returns have fallen short of “cash under the mattress” in only 0.8 % of all 25-year holding periods across the dataset. When adjusted for inflation, the incidence of under-performance rises to just 7.5 %. The few exceptions occur in highly unusual historical cases, such as Ireland in the early to mid-19th century or Japan after its 1990 equity peak.
By contrast, shorter investment horizons tell a different story: the Deutsche Bank analysis shows that in 13.6 % of all five-year windows, global stocks declined on a nominal basis. The findings highlight that timing entry and exit points can significantly affect outcomes, particularly when valuations are elevated at the outset. The report points to key measures of valuation, including the cyclically-adjusted price-to-earnings ratio (CAPE) and forward P/E, as reliable warning signals for weaker future returns. For example, the forward P/E for the U.S. S&P 500 recently exceeded 23, placing it well above long-run averages.
The bank’s strategists note that low dividend yields among equities compound the valuation risk. Whereas a few dominant stocks have historically generated the lion’s share of global equity wealth, the majority of listed companies underperformed one-month U.S. Treasury bills from 1990 to 2018, according to research by Hendrik Bessembinder. This underscores the importance of portfolio diversification and long-term commitment rather than stock-picking.
Despite the current backdrop of high valuations, inflation concerns, and geopolitical uncertainty, the report encourages investors to maintain equity exposure for long-term goals. The argument rests on equities’ alignment with global economic growth and inflation-adjusted earnings over decades. While bonds outperformed stocks in 22 % of long-term periods, the researchers emphasise that entering fixed income at the wrong point in its cycle can lead to extended under-performance.
The implications for risk-aware investors are clear: holdings in broad equity indexes tend to offer better long-term outcomes than cash or bonds when held over two or more decades. The report does caution, however, that elevated valuation today may moderate near-term returns. It suggests using market pull-backs as opportunities to rebalance rather than timing exits. Over shorter horizons, investors face meaningful downside risk, but for those with the patience and horizon, stocks remain the most effective vehicle for real wealth accumulation.
