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Diversification and asset allocation
Markowitz 1952· Concept
Mainstream viewMost economists and practitioners agree.
Diversification spreads money across many holdings and asset classes so no single loss sinks the portfolio; asset allocation sets the mix.
See it on the Money & Finance map →How it works
Harry Markowitz's 1952 paper 'Portfolio Selection' showed that what matters is how holdings move together: combining assets that don't move in lockstep lowers overall swings without necessarily lowering expected return. Owning 20 to 30 stocks removes much single-company risk; an index fund removes nearly all of it. Market-wide risk remains. Asset allocation, such as 60% stocks and 40% bonds, sets the bigger tradeoff between growth and drawdown. Rebalancing brings drifting weights back to target.
Why it matters
Often called finance's only free lunch: less risk for the same expected return. Markowitz shared the 1990 Nobel Prize in economics for it.
Think of it like
Like owning buildings in several cities and property types, so one tenant's bankruptcy or one market's slump cannot sink the portfolio.
Facts, rules and data
Markowitz (1952), Evans and Archer (1968) on how risk falls as stocks are added, and decades of return data on diversified portfolios.
Debates and risks
In 2022 stocks and bonds fell together; whether bonds still cushion stocks when inflation is high is now debated.
Connections (3)
▸Diversification and asset allocation traditionally pairs stocks with Bonds: lending money in exchange for interestMainstream view
The connection
High-quality bonds have often risen or held steady when stocks fell, because investors flee to safety and the Fed cuts rates. That made the 60/40 stock-bond mix the classic balanced portfolio. In 2008 the broad US bond index gained about 5% while the S&P 500 lost 37%.
When and why
Pension and endowment practice from the mid-1900s; tested in 2008, when it worked, and in 2022, when stocks and bonds fell together.
How solid is the link?
Return data: the Bloomberg US Aggregate bond index rose about 5% in 2008 and fell 13% in 2022, when the S&P 500 lost 18%.
Debates and risks
Whether the negative stock-bond correlation of 2000–2021 was the exception: before 2000, especially in high inflation, the two often moved together.
▸Diversification and asset allocation spreads money across Asset classes: the menu of investmentsMainstream view
The connection
Asset allocation spreads money across classes whose returns don't move in step, which sets the portfolio's expected growth and its worst drop. In 2007–09, an all-stock US portfolio fell about 51% including dividends; a 60/40 stock-bond mix fell roughly 30–35%.
When and why
Markowitz (1952) set out the theory; David Swensen's Yale 'endowment model' from 1985 extended it to alternatives.
How solid is the link?
Studies such as Brinson, Hood and Beebower (1986) and Ibbotson and Kaplan (2000) find allocation explains most of a portfolio's ups and downs over time.
Debates and risks
How far to trust historical correlations, and whether alternatives truly diversify or just report smoothed prices, are debated.
▸Diversification and asset allocation lowers Measuring risk: volatility, drawdown, recovery timeMainstream view
The connection
Mixing assets that don't move together lowers volatility. Two assets that each swing 20% a year, held half and half with no correlation, swing only about 14% combined; if perfectly correlated, still 20%. Drawdowns usually shrink too. Diversification cannot remove market-wide risk, only company- and asset-specific risk.
When and why
Markowitz (1952); William Sharpe's 1964 model separated market risk from diversifiable risk; Evans and Archer (1968) measured it with real stocks.
How solid is the link?
Portfolio math, and return histories showing diversified portfolios with shallower drawdowns in crises such as 2008.
Debates and risks
In panics, correlations jump toward one just when protection is needed; how much diversification helps in a true crash is debated.