At The Money: Focusing on Growth (Not Market Cap) with Rob Arnott, RAFI (May 7, 2026)
Indexes are weighted by their size, primarily market cap. Research Affiliates’ latest index focuses on Growth, rejiggering these indexes based on how fast companies are growing.
Full transcript below.
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About this week’s guest:
Rob Arnott is known as the “godfather of smart beta” and founder of Research Affiliates, which oversees strategies for over $100 billion in assets.
For more info, see:
Professional Bio
Masters in Business
LinkedIn
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TRANSCRIPT: Rob Arnott on the Research Affiliates Growth Index
Intro
Take a load off Fanny
And (and, and) you put the load right on me
(You put the load right on me)
Barry Ritholtz: Traditional market-cap-weighted indexes like the S&P 500 have really done a great job in dominating investor inflows. But today there are concerns that cap weighting is leading to increased market concentration into just a handful of stocks, especially the Mag Seven, higher valuations, and increased risks for investors. How should an index investor think about this? Well, to help us unpack all of it and what it means for your portfolio, let’s bring in Rob Arnott, founder of Research Affiliates. The firm recently put out the Research Affiliates Growth Index, which is different from both cap-weighted ETFs, but also different from equal-weight ETFs.
Barry Ritholtz: So I’m fascinated by this index, which you guys put out. You’re tracking it live today. It’s not yet investible, but I assume there’ll be an ETF out sooner rather than later. Define Raffi. Define the Research Affiliates Growth Index. What are the weights based on? How do you think about alternatives to cap-weighted growth?
Rob Arnott: Sure. Let’s back up just a little bit and challenge one of the basic principles of modern investing and modern finance—the principle that there’s this binary duality of growth and value. If it’s not value, it’s growth. If it’s not growth, it’s value. Pardon me? Those are not one-dimensional. Those are two dimensions. You can have cheap and expensive. You can have fast and slow growing—two completely different dimensions. Our industry has had a fixation on this simple duality, where if it’s cheap, it’s value, and if it’s expensive, it’s growth. No, if it’s expensive, it’s expensive—it’s much simpler. If it’s growth, it’s growth.
Rob Arnott: So to my astonishment, looking back, cap weighted indexing goes back to the fifties as investible portfolios, and growth indexes to the late seventies, and investible growth strategies to the 1980s. Nobody has posed the question, why don’t we look at this fundamentally? Instead of based on valuations, nobody has asked the question, why don’t we create an index that chooses growth stocks based on how fast they’re growing and weights growth stocks based on how big their dollar contribution to the growth of the macro economy is? If you do that—if you choose companies that are growing rapidly and you weight them on the dollar magnitude of that growth—you wind up with an index that over the last 30 years would’ve outperformed Russell Growth by four and a half percent per annum going back almost 30 years.
Barry Ritholtz: Russell Growth, not Russell Value.
Rob Arnott: Correct.
Barry Ritholtz: So if that’s the case, what are we selecting on? It’s not just cap weight, I’m assuming. And I’ve read some of the research—you’re looking at increasing sales, increasing profits, increasing R&D. Explain what goes into the Raffi Growth Index.
Rob Arnott: Sure. Well, there’s an article coming out in the next issue of the Financial Analyst Journal that takes a deep dive. So anyone who’s got access to the FAJ, take a look. For the moment, you can also find it on SSRN—just look up “Arnott Fundamental Growth” and it’ll take you right there. Anyway, if you wanted a growth index that didn’t anchor on expensive stocks but anchored on fast growing companies, how would you instinctively choose to measure that growth? Sales, profits—those are the obvious choices. Slightly less obvious: most growth companies have R&D, and it’s a big enough part of their business that they break it out as a separate item in their P&L. So what about growth in R&D? Because if they’re shrinking their R&D budget, that’s a bad sign. So if you have three different growth rates—growth in sales, growth in profits, and growth in R&D spending—if R&D is available, use all three; if not, use two of the three. You average those growth rates and you’ve got a very good gauge of how fast the company is growing. If it’s growing rapidly enough to be in the top 25%, let’s use it.
Rob Arnott: Here’s a fun factoid: two of the Magnificent Seven don’t make the cut for the Raffi Growth Index.
Barry Ritholtz: Huh? Really? Which two?
Rob Arnott: Take a guess.
Barry Ritholtz: So who’s cutting way back on their R&D and not seeing increases in revenue? Apple and Amazon. I’m just spitballing.
Rob Arnott: You got one out of two.
Barry Ritholtz: So Apple is the first one. Amazon?
Rob Arnott: Amazon. Amazon and Microsoft. Both were growing incredibly fast in the 2010s and have been growing nicely in the 2020s, but not fast enough to make the cut. So they’re left out of the Raffi Growth Index.
Rob Arnott: The index is on Bloomberg—it has been since last March—and it’s already 13 percentage points in less than a year ahead of Russell Growth. So the idea works and it’s exciting. I wish I was on your show to announce that it’s an investible ETF or mutual fund. Not yet.
Barry Ritholtz: When it comes out, when it becomes investible, we’ll have you back. I want to ask you a question about dollar magnitude as opposed to percentage magnitude of growth. Every metric I see is almost always a percentage. You are looking at absolute dollars of growth. Explain the thinking behind this. How does it manifest in performance? How does it work?
Rob Arnott: We select based on percentage growth. You could have a huge company that has sales grow by a hundred billion in a year, and it’s only 10% growth—right? Or 5% growth. And if that’s the case, it’s not a particularly fast-growing company. So percentage growth is used to choose the companies. Now, the two biggest stocks in Raffi Growth are Nvidia and Apple. One has had stupendous growth from a low base. One has had good growth from a high base. Both have had percentage growth fast enough to make the cut. They are both a little over 10% of our index. Now, think what that means. If it’s a 10% weight, that means Nvidia has singularly, all by itself, been 10% of the sales or profit growth in the aggregate US economy.
Barry Ritholtz: Wow.
Rob Arnott: Huge. Apple has been 10% of the aggregate growth in sales or profits of the US economy. So by weighting companies in proportion to the dollar magnitude, you’re not going to introduce a bias toward frothy tiny companies that have had just a big percentage surge. You could have a tiny company that’s grown tenfold, and if you weight it by that tenfold growth, it’s going to get a huge weight—and it’s a tiny company. It might be a flash in the pan.
Barry Ritholtz: So in other words, the percentage gains matter, but so too do the real dollar gains.
Rob Arnott: Exactly right.
Barry Ritholtz: I understand that. So I’m curious about the volatility of this versus traditional cap weighting indexes. How does this compare? Are you getting better performance, but you have to live with a little more volatility?
Rob Arnott: The short answer is you have to live with a little bit more volatility, and you have to live with occasional periods when it will underperform. On average over the last 28 years, it adds four and a half percent a year, plus or minus 7%. So in just a normal disappointing year, it’s going to underperform by about two. In a normal, excellent year, it’s going to outperform by about 12. So since we launched last March, the 13% outperformance means this is a very typical, very normal good year. You have to be willing to take a little bit of volatility, but if you go back, you find that it wins about seven out of 10 years.
Barry Ritholtz: Wow. That’s pretty cool, to say the very least. So, since we’re talking about a lot of, not just large-cap companies, but companies with a substantial economic footprint, my assumption is there aren’t a whole lot of capacity or liquidity constraints. I’m assuming this can ramp up just like an S&P index or what have you.
Rob Arnott: Short answer to your question is, current AUM is zero, so there’s loads of capacity. Longer answer: An educated guess would be that it has about four times the turnover of the S&P, maybe five. So just on that alone, its capacity would be a fourth or a fifth of the S&P. It’s also tilted toward a particular category, not the whole broad market—so that would suggest another haircut. I think its capacity would be 10 to 20% of the S&P. Given that there’s about 15 trillion indexed to the S&P, that would give us something on the order of one and a half to 3 trillion as a capacity.
Barry Ritholtz: So plenty of capacity. Last question. I’ve been watching various narratives come into favor and then fade. We went through a whole blockchain crypto set of narratives. AI seems to be in the midst of its various narratives. When you think about the Research Affiliates Growth Index—the fundamental growth index—does the dominant narrative matter, or is it just redefining its constituents based on what is best working today, what is seeing the highest increases in revenue, profits, and research and development spending?
Rob Arnott: Well, between Raffi—the fundamental index, which has a stark value tilt—and Raffi Growth, which has a stark growth tilt, I like to think that we’re launching a revolution in indexing. I mean, the runway for this is huge. One other observation: we’re quantitative investors. We love testing things. Quantitative investors are addicted to data mining—go back historically and ask, what can I construct that’s worked? We don’t do that. The scientific method means you start with a hypothesis and you only use the data to test the hypothesis. Our hypothesis was: if you select companies on how fast they’re growing and weight them on the magnitude of their contribution to economic growth, this is an idea that might work pretty darn well. And lo and behold, it does. The back tests of Raffi when we launched it 20 years ago showed about 2% value add relative to the cap-weighted value. It’s added two to two and a half percent live for 20 years. So you don’t fall into the trap of creating a strategy that looks great in a back test and falls apart instantly.
Barry Ritholtz: I’m so glad you said that, because when do you ever see a bad back test? All back tests are great, that you—
Rob Arnott: I see lots of bad back tests.
Barry Ritholtz: Oh, no. I mean the ones that get—
Rob Arnott: And I would never promote it.
Barry Ritholtz: The back tests that get shared are the ones that—of course they are. Totally. And inherent in every back test is the concept that the future is going to look like the past. And very often we see the future does not look like the past. So the back tests fail. Many back tests that look great fail to perform in real life.
Rob Arnott: That’s exactly right. Because the world changes. And if you’re doing a back test to create a better back test—
Barry Ritholtz: Right. That’s right.
Rob Arnott: That’s the epitome of data mining, and it’s endemic in our business.
Barry Ritholtz: Absolutely. So Rob, when this comes out as an investible product—be it an ETF or an SMA or a mutual fund—come back, tell us about it.
Rob Arnott: I’m not sure it will, because I’m trying to keep it secret. It’s so good.
Barry Ritholtz: Well, you and Jim Simons—like, kick out all the outside investors and just keep your own money so it works well. So to wrap up: if you’re concerned about cap weight, if you’re concerned about market concentration or valuation, take a look at the Research Affiliates Growth Index. It’s not market cap weighted, it’s not yet investible, but I know Research Affiliates and I’m pretty confident there will be an ETF for you to put money into at some point in the future. I’m Barry Ritholtz. You’ve been listening to Bloomberg’s At the Money.
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