$SPDR Dow Jones Industrial Average ETF Trust(DIA)$
Mathematical Money | October 9, 2026
Two things are true at the same time right now and they shouldn't be. $SPY$ and $QQQ$ both set record closes on Tuesday and sit within one percent of them tonight. $DIA$ peaked on 5 August and has fallen about 6% since, with no bounce worth the name in between.
Most of the commentary I've read explains this as old economy versus new, or value versus growth. I went and did the arithmetic instead, and the answer turns out to be much more specific than that. A third of the Dow's entire decline is one company.
First, the thing almost nobody checks
The Dow is price-weighted. Not weighted by company size, by share price. A company whose stock trades at $1,000 carries roughly ten times the influence of one trading at $100, regardless of whether the second company is worth five times as much.
It's a genuinely odd way to build an index and it survives mostly because it's been done that way since 1896. But it means you cannot reason about the Dow the way you reason about the S&P. In the S&P, a company matters because it's big. In the Dow, a company matters because its shares happen to be expensive.
Goldman Sachs was trading at $1,060 on 5 August. That made it roughly 12% of the entire index on its own, more than any other member, not because it's the biggest business in there but because it has the highest share price.
The attribution
Here's the sum. For a price-weighted index the contribution of each stock is simply its dollar price change divided by the sum of all thirty starting prices. I ran it from the 5 August peak to tonight's close, and the model reproduces the Dow's actual move to within a tenth of a percentage point. The method holds.
Goldman fell from $1,060 to $884, a drop of 16.6%. That single move took close to two full percentage points off the index, which is a third of the entire decline.
Add in the rest of the financials, meaning JPMorgan, American Express, Travelers and Visa, and the bloc accounts for roughly half of everything the Dow has lost since August. Home Depot, Caterpillar, Sherwin-Williams and Boeing did most of the rest, with Boeing down 22.5% and Home Depot down 18.3%.
The four big technology names inside the Dow went the other way entirely. Microsoft, Apple, Nvidia and Salesforce together added about a percentage point over the same stretch. So the index didn't fall because its tech was weak. It fell because it holds a very expensive bank.
So why did those particular companies fall?
This is where it stops being an indexing quirk and starts being useful. Look at what has happened since 1 August across the market, not just inside the Dow.
Real estate is down about 10%, measured either through $VNQ$ or $XLRE$. Regional banks are down 9.2%, utilities are off 6.9%, industrials 6.8%, financials 5.4%, and long-dated Treasuries themselves have lost 6.0%. Over the identical period technology rose 13.7%, energy gained 8.9% and healthcare 3.1%.
That is not a growth-versus-value split and it isn't about AI either. The dividing line is funding dependence. With the 10-year trading above 5.2% and the 30-year above 5.5%, every business that needs the capital markets got repriced: lenders whose margins depend on the curve, property that is valued off a discount rate, utilities that compete with bonds for income buyers, industrials that sell equipment on finance, and banks whose deal pipelines dry up when money costs this much.
Businesses that fund themselves out of their own cash flow didn't notice at all. The large technology companies are sitting on net cash and finance their own investment, so a twenty-four year high in long yields is, to them, somebody else's problem.
$GS$ is the purest expression of that. Capital markets revenue, deal financing and balance sheet funding all key off the long end, which is why it fell further than any other large bank and why, at a share price that size, it took the index down with it.
What this actually means, honestly
I want to be careful here, because the obvious conclusion is the wrong one. The tempting read is that the Dow is cheap and due a bounce, and I don't think that follows. Nothing in the last two months has been irrational, and the thing that caused it, a long bond yielding north of 5%, has not changed. Cheap because rates are high is a condition, not a catalyst, and buying a rate-sensitive business while rates are still rising is just taking the other side of a trade that is currently working.
The second tempting read is that this is a warning that the whole market is about to roll over. Also not something I'd lean on. Narrow markets can stay narrow for a long time and plenty of people have gone broke being early to that call.
What it does change is how you read the index. When the Dow is down 6% and one stock is a third of it, "the Dow fell" tells you almost nothing about the thirty companies in it. Ten of the thirty are actually higher than they were in August.
The part that matters for anyone selling options
Here's the bit I find genuinely useful, and it's measurable. The S&P's realised volatility over the last sixty days is running at about 11%. The ten individual stocks I hold long-dated calls on average roughly 52% over the same window. The index is nearly five times calmer than its own components.
That isn't because anything is calm. It's because the components are moving violently in opposite directions and cancelling each other out inside the average. Storage and banks fell double digits in the same fortnight that power and semis rose double digits, and the index absorbed both and barely twitched.
If you sell index premium, that's a comfortable environment and it's being paid reasonably. If you sell premium on single names, you're collecting on volatility that is genuinely there, and that's a much better trade than it looks from the index level. What you should not do is assume the calm index means your individual positions are calm. Mine certainly haven't been.
What would change my mind
The long end, and nothing else. If thirty-year yields come back below 5%, the entire punished complex re-rates quickly and the Dow's composition goes from a liability to an advantage. Until then I'd read the index for what it actually is, which is a weighted average of thirty share prices currently being dragged around by the most expensive one.
Two things I'd like other views on.
Does the price-weighting bother anyone else as much as it bothers me? I understand the history, but an index where a stock's influence depends on whether management ever did a split seems like a strange thing for the financial press to quote every evening.
And on the volatility gap. If index vol is 11% and single-name vol is 50%, where are you actually selling? I've been doing both and I'm increasingly convinced the single-name side is where the compensation is, but it comes with assignment risk the index version never has, so I'm not sure the comparison is fair.
#DowJones #GS #markets #volatility #options
Stop guessing. Start calculating.
Live to fight another day. đ¤
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