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Comment by zzleeper | Hacker News Reader

You made me think. The weights of e.g. the SP500 are not ideal then.

Berkshire is in the SP500, but so are Apple, Coca Cola, Amex, BoA, etc. which are Berkshire largest investments. So if Coca Cola has an idiosyncratic hit, then you get hit twice by it: first in your KO holdings, then in your BRK.A holdings.

At the extreme, if there is a company that then invests in Berkshire and so on, you could end up overweighting a lot certain firms. Also, isn't there double counting in terms of the stock market cap?

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No. The S&P 500, like most other market-cap-weighted indexes, uses float-adjusted market cap, meaning that they exclude shares owned by other public companies when computing the weightings. So the fact that BRK.A owns shares in other companies in the index is accounted for; you don't get double counting, and so your exposure is not inflated.

You're right on float adjustment. But shares of coke held by Berkshire are still considered part of float.

The S&P considers the shares of Coke held by Berkshire to be excluded from the float. S&P's float adjustment methodology is described here [1]:

"Float adjustment excludes shares that are closely held by control groups, other publicly traded companies, government agencies, or other long-term strategic shareholders."

[1] https://www.spglobal.com/spdji/en/documents/index-policies/m...

> So if Coca Cola has an idiosyncratic hit, then you get hit twice by it

I think that is neglibile, depending on how big you define a hit. If Burger King gets hit, that will probably effect Coca Cola as the largest supplier (just saying it like that, don't know if they really have that kind of business with each other), too.

There's lots of dependency in the modern world, I don't think it really matters.

edit: If Coca Cola does well, you profit twice. Maybe see it that way... ;-)

It might be if your investment strategy was to allocate equal amounts to each sector, but that's not how most passive funds work. Instead, they allocate based on market-cap weighted basis, which means there's no double-count going on.

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