Thomas Piketty's Capital in the 21st Century discusses this. In Part three, chapter "Global Inequality of Wealth in the Twenty-First Century", he notes two reasons why large fortunes see greater returns
... a person with 1 billion euros has greater means
* to employ wealth management
* to take greater risks and be patient
Data shows that large fortunes grow at consistently higher return rates vs average fortunes.
More than 800 public and private US universities manage their own endowments - totaling $400B in assets among them.(p. 447)
Conclusions from public reports on these endowments:
1. The return on US university endowments has averaged 8.2%a year from 1980 to 2010.
2. The return increases rapidly with SIZE OF ENDOWMENT
- for 60 universities with > $1B , average r=8.8% - twice as much as less well-endowed universities.
You see diversified portfolios across these endowments. That's where the similarity ends. In the larger endowment funds, you see 'alternative investment strategies' such as shares in private equity funds, derivatives, real estate, and raw materials. These alternative investments represent just 10% of the smaller uni funds, but comprise >60% of the endowments above $1B.
Piketty concludes that it's these alternative investments that enable the largest endowments to obtain 2x the return as smaller endowments - e.g. 10% annual r vs 5%. This persists year to year.
How is this possible? Piketty explains that it's about economies of scale in portfolio management. Harvard (with $30B in assets) spends $100M a year on management - or .3% per year. OTOH, a $1B fund couldn't afford to pay $100m in management fees - that'd be an unsustainable 10% fee. All of their gains would go to management fees. In practice, no endowments spend > 1% in fees - typically they are under .5%.
I had to read this section a couple times as it seemed to fly in the face of our conventional wisdom here on MMM. However, I think the thing to note is that the difference in returns occurs for fortunes >> $1B - which is way outside of our worlds.
Anyway - that's what I learned about this topic in Piketty's book.