Building a Diversified Portfolio
Practical portfolio construction across asset classes, and Malkiel's take on international diversification and real estate.
Beyond the core stocks-versus-bonds allocation covered in the life-cycle chapter, Malkiel walks through building out a fuller diversified portfolio — adding international stocks alongside domestic ones, since different countries' equity markets don't move in perfect lockstep, and real estate (through REITs, real estate investment trusts, rather than direct property ownership for most investors) as a further diversifying asset class with somewhat different return drivers than either stocks or bonds.
The organizing principle across all of it is the same one from earlier in the book: assets whose returns aren't perfectly correlated with each other reduce a portfolio's overall volatility for a given expected return, even when none of the individual assets is picked for any special insight into its own future performance — the diversification benefit comes from the combination, not from any single component being individually superior.
Malkiel is candid that the diversification benefit from international stocks specifically has become somewhat less powerful over time as global capital markets have become more interconnected — correlations between major developed markets tend to rise, sometimes sharply, exactly during the periods of global stress when diversification would be most valuable, even though it still holds up meaningfully over full market cycles. He treats this as a reason to keep expectations realistic rather than a reason to abandon international exposure altogether — a diversification benefit that shrinks somewhat during crises is still preferable to no diversification benefit at all.
| Asset class | Role in the portfolio |
|---|---|
| Domestic stocks | Core long-run growth engine |
| International stocks | Diversification — doesn't move in perfect lockstep with domestic markets |
| Bonds | Lower volatility, income, and a shock absorber against stock declines |
| REITs | Real-estate exposure with different return drivers than stocks or bonds, without direct property ownership |
Malkiel pairs the diversified-allocation recommendation with periodic rebalancing — selling a portion of whichever asset class has grown to be overweight relative to the target allocation, and buying more of whichever has become underweight, restoring the original target mix on a regular schedule (annually, for instance). The behavioral value of this discipline is that it forces a mechanical version of "buy low, sell high" — trimming an asset class after it has risen and adding to one after it has fallen — without requiring the investor to make any active judgment call about which asset class is about to do better, sidestepping the same behavioral traps covered earlier in this course.
Imagine a target allocation of 60% stocks, 40% bonds. After a strong year for stocks, the portfolio drifts to 68% stocks, 32% bonds. Rebalancing means selling enough stock to return to 60/40 — mechanically selling the asset that just went up and buying the one that lagged, without the investor needing any view at all on what either asset class will do next.
The deeper logic behind rebalancing is worth making explicit: it does not require the investor to predict which asset class will outperform next, only to accept that asset classes that have recently risen a great deal relative to a target allocation have, by definition, become a larger and more concentrated share of total risk than originally intended. Trimming back to target is as much a risk-control discipline as a return-enhancing one — it is the mechanism that keeps the portfolio the investor actually chose from silently drifting into a different, unintended one purely as a byproduct of different asset classes compounding at different rates.
Malkiel also notes the discipline cuts against a natural behavioral pull in the opposite direction — investors instinctively want to add more to whatever has recently performed best, the same chasing-performance bias documented in the behavioral finance chapter earlier in this course. Rebalancing is, in effect, a mechanical precommitment device that overrides that instinct before it has a chance to influence a live decision.
- A fuller diversified portfolio extends beyond domestic stocks and bonds to include international stocks and real estate (via REITs).
- The diversification benefit comes from combining assets whose returns aren't perfectly correlated, not from any single asset class being individually superior.
- Periodic rebalancing back to a target allocation mechanically enforces buying low and selling high without requiring active market-timing judgment.
- International diversification's benefit tends to shrink during periods of global market stress, when correlations rise — still real over full cycles, but not a guarantee during a crisis.
- Rebalancing functions as risk control as much as return enhancement, and acts as a precommitment device against the instinct to chase whatever asset class just performed best.