Indices are supposed to reflect a part of the market. That's why you have all of S&P500, the Dow, NYSE Composite, and Nasdaq Composite (and several others) in the US — They each reflect different attributes of the market as a whole.

As it stands, it's clear that the users of S&P500 are not interested in the performance of the parts of the market made up of overpriced (and potentially highly volatile) IPOs.

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tristanj 4 hours ago | parent [-]

The problem with your framing of "users of S&P500 are not interested overpriced IPOs" is that it conflates two fundamentally different things: what an index describes vs what investors prefer. The moment you start filtering out parts of the market based on investor appetite vs market reality, you stop building an index and instead start creating an actively managed product. That's active investing. It's no longer an index.

The S&P 500 is used as the benchmark of the market by practically everyone. Journalists, policymakers, investment managers, politicians, regular investors, everyone I know. If the benchmark that everyone uses as a market proxy is systematically excluding a substantial part of the market, then the gap betweeen "the index" and "the market" has real consequences.

You can't have it both ways: Either the S&P 500 is a market proxy, in which excluding parts of the market is a problem; or it's a curated slice, in which everyone needs to stop it as the default benchmarket for the market.

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ywvcbk 15 minutes ago | parent | next [-]

> what an index describes vs what investors prefer

What makes you think S&P 500 did not become the most popular index (instead of full market ones) because of the rigid entry criteria and and rules for weights.

Amongst other things the weighting is not even based on the market cap.

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f33d5173 4 hours ago | parent | prev [-]

An index is an index. It works fine as an index if it excludes one or two stocks. People seem to forget as well that this is a question of waiting a single year before it including the stock. It is literally just long enough to make sure the price settles, it's not some catastrophic thing.

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tristanj 3 hours ago | parent [-]

> it excludes one or two stocks.

It's more than that. None of SpaceX, OpenAI, nor Anthropic will meet the criteria, and they will make up a significant part of the US stock market. Each of these companies is heavily investing their cashflow into growing the company and are unlikely to be profitable many years.

The inclusion criteria prioritizes companies that extract their cashflow into profit, and excludes companies that invest their cashflow into growing the company. For example, when Jeff Bezos ran Amazon he described his company as "famously unprofitable, And that is a conscious strategy and an investment decision." Amazon only joined the index in 2005, nearly 8 years after IPO, even though it was a significant member of the stock market at the time.

	▲	tankenmate 2 hours ago \| parent \| next [-]
		"The inclusion criteria prioritizes companies that extract their cashflow into profit", in almost all cases, yes. But if you want to buy into these newer stocks there are various high growth indices you can buy, no one is stopping you. If you want to buy into only one or two of those stocks then you can. It's a free market for stocks and it's a free market for indices. There's no regulation that says the S&P has to include certain stocks.
	▲	ab5tract an hour ago \| parent \| prev [-]
		And that approach famously hurt investors, the economy, and/or Amazon in what specific ways, exactly?