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Comment by FabHK | Hacker News Reader

There are certain criteria, see [1] or [2] for a summary. They need to be publicly traded for sufficient time, have sufficient free float, be profitable, etc.

See [3] for example on why Tesla isn't.

[1] https://us.spindices.com/documents/methodologies/methodology...

[2] https://en.m.wikipedia.org/wiki/S%26P_500_Index#Selection_cr...

[3] https://seekingalpha.com/article/4088016-will-tesla-join-s-a...

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Yep. So, you don't just own the top 500 stocks by market cap. You own a set of stocks that resemble that idea, but are in fact still choices made by S&P. Also notice that stocks don't immediately get dropped when they fall below that criteria; there's a buffer for how bad they have to get to be dropped. Additionally, the rules governing these choices are free to change at any time. For example, whether stocks with split voting shares should qualify is still a discussion.

Let's also not forget Hacker News's favorite law: Goodhart's Law. The S&P has performed wonderfully well when it was observed as an index. But now that it's a target, the world will change around it.

It’s a huge stretch to say the S&P 500 isn’t the current top 500 stocks by market cap just because they don’t include several recent IPOs and have discretion to exclude stocks based on potential stock manipulation. These are very rare cases that have little affect on the overall index. In time (not instantly) they add large established companies. Proportions are always weighted directly to market cap percentage. They’re not weighing some stocks higher than others like how an active manager would allocate.

Agree “beating the index” is quite a joke since that is the benchmark for fund performance and so much money is passive invested now. Matching the index performance is saying “our fund equities have appreciated on equal basis to how all others have”.

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