In an attempt to contribute something new, I will hew pretty strictly to the approach used in Parts 1 and 2: given some expected return, standard deviation, and correlation for gold, how much diversification benefit might one expect from adding gold to an all stock portfolio?
Gold—the ultimate diversifier?
Probably not.
If I had a dollar for every journalist who quoted some expert who said that “you should keep 5% of your portfolio in gold for diversification,” I’d have enough for a very good bottle of California Cabernet.
More legitimately, the Permanent Portfolio has been around for quite a long time, with a substantial allocation to gold. (see this post by nisiprius: viewtopic.php?p=7157009#p7157009)
A rational newcomer to investing might suppose, given the number of mentions in the press, that there must be something to the idea of holding gold as part of a portfolio. But wishing and hoping doesn’t make it so.
Let’s start with the obvious argument AGAINST the use of gold to diversify a stock portfolio.
1. Gold is a store of value
2. To store is to keep, maintain, and preserve unchanged
3. To store is NOT to grow and NOT to lose; it is to KEEP
4. Therefore, the expected value of gold, in real terms, is the same tomorrow as today; the same next decade as last decade; the same one hundred years from now as … oh wait: gold has only been a traded asset since 1971, after the collapse of the Bretton Woods agreement, the true end of the gold standard, which had held for centuries until that first thunderous crack in February 1934.
Anyway, you get the idea: over the very long term, the expected real return on gold is exactly zero (minus storage costs). If that statement is not true, then it cannot be true that gold is a store of (real) value.
I believe gold to be a store of value. Full stop.
I also believe that productive business enterprises CREATE value, rather than store it, and that when I buy a broad stock market index fund, I own a share of global value production, and can reasonably expect to see the value of that stock investment grow in real terms over time, as those productive enterprises of which I own a share continue to create value.
Therefore, addition of gold to a stock portfolio may have a diversification effect, in terms of reducing portfolio standard deviation; but will almost certainly NOT be able to enhance portfolio return. Gold might function as a stabilizer, analogous to short-term TIPS, delivering inflation as their only return. Which means that an allocation to gold—or to short-term TIPS-- must necessarily drag down the long term return on holding 100% of the portfolio in shares of productive enterprises which CREATE value.
In addition, the reduction in portfolio standard deviation from holding gold is likely to be less than that for holding short-term TIPS, because gold is more subject to speculative influences, hence swings about to an even greater degree than the inflation expectations that drive the price of short-term TIPS.
H1: Low return + high volatility = inferior diversifier, relative to, say, an intermediate bond fund.
UNLESS … there is some unsuspected magic in negative correlation, whereby addition of a small allocation to gold both reduces portfolio standard deviation AND increases portfolio geometric return, per the analyses in Part I of the thread.
That is the question to be investigated in this post.
The data
I’ve been using SBBI data from 1926 throughout these threads. That’s not going to work here in Part 3. The dollar price of gold was constant from December 1925 to February 1934, when it leaped by about 75% in a day (~$20 -- $35), after which it was constant again through the late 1960s, after which it exploded for a decade after Nixon took the dollar off gold.
Beastly series to analyze; accordingly, I begin the data series anchored to the end of 1972 (which is also when Total Bond returns become available). This allows about eighteen months for the initial pricing chaos, post delinking of the dollar to gold in August 1971, to settle down.
*You could alternatively begin the gold series in 1792 same as my stock and bond series, where the gold price would be constant and annualized return would be zero until 1934, excepting two small revaluations in in the 1830s and 1840s, and temporary deviations in 1814 and 1862-79. By temporary I mean the positive paper dollar returns initially received were exactly reversed once the movement in these periods was concluded, i.e., gold price at t-begin = price at t-end = ~$20 per ounce = ~1792 price.
*But adding back 140 years of 0% returns is probably not going to be acceptable to the investor seriously contemplating whether to add gold to their portfolio in 2023; that stretch of returns data will be dismissed as “ancient history.” No problem, I won’t go there.
For the fifty years through 2022, the inputs to the Markowitz analysis are as follows. In contrast to prior threads, for this exercise I will use exact historical amounts to the fourth decimal for return and SD. Gold price is from Simba, London pm fixing.
Stocks: arithmetic return = 11.85%, SD = 17.51 *
Gold: return = 9.59%, SD = 26.83%, correlation with stocks = negative 0.21.
*BTW, only periods that include the crash of 1929-1933 give a stock SD greater than or equal to 20%; the 130 years before and the 90 years after typically run an SD of 12% to 18% over twenty-year windows, see https://papers.ssrn.com/sol3/papers.cfm ... id=3805927.
In short, for these fifty years gold had a somewhat lower return, was rather more volatile, and did indeed have a negative correlation with stocks.
Here is the Markowitz chart*
*Because the kluge—geometric return = AR + ½ variance—is increasingly inaccurate for SD over 20%, for this chart the vertical axis is also computed using the approximation labeled QE in Markowitz. It’s still not exact, but it is closer. For comparison the kluge is also shown (solid blue line).

Whoa—that looks quite a bit different than the stock - bond charts we saw in Part 2 of this thread.
Good news: a small allocation to gold could have reduced standard deviation substantially, and—very slightly—increased geometric return. By about 7 basis points at the peak. The stock investor desirous of achieving risk reduction without any reduction in return could justify up to a 30% allocation to gold.
Next, I add the total bond-stock risk return line for this period, using the exact 50-year returns: AR for Total Bond = 6.76%, SD = 7.12%, correlation = .34. As before, a very positive return-risk ratio, with risk far less than stocks or gold, and correlation with stocks moderately positive, i.e., none of that negative correlation benefit with total bond.

The orange line is below the blue and gray lines down through a 50-50 allocation to stocks and gold. Gold is the superior diversifier in that range. However, a 50-50 allocation performs identically to an 80-20 stocks/total bond allocation. At all lower stock allocations, a mix with total bond provides the same return as a mix with gold, for lower risk.
There you have it: the diversification benefit of gold, such as it is, based on the exact series of returns for the cherry-picked 50-year period December 1972-2022.
Hmm, I think you know where this is going.
A rational skeptic of gold might opine: “If the paper dollar price of gold was artificially constrained for decades, I don’t think pegging the start of the price series to seventeen months after the collapse of Bretton-Woods is quite enough time for a new equilibrium to be established.”
Okay; what if we started the series 10 years later, at the end of 1982? Forty years still qualifies for the “long run,” does it not?
Whoa, says the gold advocate. “You are throwing out the baby with the bathwater. Sure, go ahead and arbitrarily exclude the once-in-a-century-or-two-or-three crucible that was the 1970s. Fine, wipe the (barely controlled) galloping inflation of that era from the record. I agree, the performance record for gold won’t look so good if you exclude exactly those circumstances under which gold might shine.”
Hmmm.
Without taking a stance on this dispute, it can’t do any harm to look at the 40-year record from 1982 to 2022—can it? That’s not as “much” history as the 50 years from 1972, but it is still a lot of history. In fact, my personal accumulation history tops out at about 40 years (first IRA contribution 1983, last (spousal) IRA contribution 2022). YMMV.
Might be good to know if gold is so fitful an asset that it might fail to shine throughout your entire accumulation horizon.
But:
“How nice for you,” snarks the gold advocate. “Oh, right, I remember now: the gold price last peaked in the early 1980s. How convenient. Come to think of it, my dear professor, aren’t you on record as stating that 1982 was a generational low in stock and bond prices? So you go, guy: you’ve decided to measure the performance of gold from its top and stocks from their bottom. What could be more fair?”
Got me there.
Still, no harm in looking at the post-1982 data? Right? With the caution that still other slices on the historical data might also be worth a look.
Pause for comments.