Decades of research at Vanguard and elsewhere have shown that asset allocation—how you divide assets across broad asset classes—is the primary driver of a portfolio's risk and return.
One of the most famous of these studies—"Determinants of Portfolio Performance" (1986) by Brinson, Hood and Beebower in the Financial Analysts Journal—found that asset allocation accounts for 94% of the variation in returns in a portfolio, with market-timing and security selection accounting for only 6% (Figure 1). Vanguard research by Wallick et al. (2012), Philips et al. (2014) and Scott et al. supported these findings. It showed that, over time, the asset allocation decision was responsible for between 81% and 91% of the return patterns of balanced funds available to investors in five global markets: the U.S., Canada, the U.K., Australia and Japan.1
Figure 1. Investment outcomes are largely determined by asset allocation
Source: Vanguard illustration, based on data from "Determinants of Portfolio Performance" (1986) by Brinson, Hood and Beebower.
A portfolio composed of broadly diversified ETFs can help ensure that performance and risk exposure are based primarily on your asset allocation decisions. In fact, holding even a small number of broad-market ETFs can provide a convenient and low-cost way to diversify across asset classes for long-term investors (Figure 2).
Figure 2. Investors can diversify across asset classes with a small number of ETFs
Source: Vanguard. Hypothetical portfolios are shown for illustrative purposes only and shall not be construed as a recommendation to buy or sell any security or financial instrument, or an offer or recommendation to participate in any particular trading or investment strategy.
Over time, the varying returns of different asset classes will cause nearly every asset allocation to change, resulting in a change to the portfolio's risk and return characteristics. That's why we believe periodic portfolio rebalancing is important. ETFs' trading flexibility and ease of access make them ideal tools for rebalancing a portfolio back to its strategic asset allocation.
Points to consider
In a diversified portfolio, gains from some investments may help offset losses from others. However, diversification does not ensure a profit or protect against a loss.
An all-index portfolio removes the potential for market outperformance that can result from active management or individual security selection.
All ETFs are subject to market risk. Global ETFs involve additional risks, including currency fluctuations and the potential for adverse developments in specific countries or regions. Fixed income ETFs are subject to interest rate, credit and inflation risk.
1 Percentages represent the median observation from the distribution of percentage of return variation explained by asset allocation for balanced funds. The results by country were as follows: U.S. 91%; Canada 86%; U.K. 81%; Australia 89%; and Japan 88%.