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I read from a paper that: "Since many transactions have multiple sending addresses, we can make the reasonable assumption that all these addresses have the same owner." (Quantitative Analysis of the Full Bitcoin Transaction Graph by Dorit Ron and Adi Shamir) So I wonder if the same could be said about the addresses taking part in a multisignature of a multisig transaction input/output.
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Multisig is useful for both a single individual and for a group. Individuals can use it to secure their funds by using a 2/3 address and distributing the keys. Groups can use multisig to implement an escrow transaction for goods or services.
These, and other use-cases, for multisig are being used today, but it's impossible to know the proportion of individual-use and group-use. There is no way to know for certain if they are controlled by the same person, unless you have more information than just what is available in the blockchain.
1If I was a betting man, I'd wager that >90% are just used by individuals, but I have no hard data to back that up, for reasons I mentioned in my answer. – morsecoder – 2017-03-14T02:37:25.413
the problem with such general statements are, that there is no underlying data, and as such are only valid for the scope of the intention of the document. Already the definition of the word "owner" comes in difficult, cause I use in our company three people for 2of3 multisig. So I would say "no", not the same owner. But then again it is the same company ('s money), as such the same owner. Very ambivalent ... – pebwindkraft – 2017-04-09T15:35:54.787