[msgilligan]

> The only way that makes any sense is if you subtract returns for sales made in a different period to the sales period you are considering

Exactly. That's the way accounting works. They did not know in the previous quarter that the product would be returned in the following quarter, so they end up having negative sales in the current quarter.

Yes it produces "garbage output", which I find amusing.

[oncallthrow]

But that isn’t how you calculate market share, so what you’re saying is nonsense.

[msgilligan]

There are multiple ways of calculating market share (e.g. units vs dollars or for different time periods) but assuming it is measured in dollars for a quarterly time period, how would you calculate the market share based upon my sample data above?

[oncallthrow]

(company sales in period - company returns for sales made in said period) / (industry sales in period)

[matt_kantor]

With this formula market share for past periods can keep changing arbitrarily far into the future (depending on the companies' return policies).

[oncallthrow]

Yes.

[msgilligan]

That is how it was calculated in a published trade magazine (either Infoworld or MacWeek, I think) I'm not sure if the the analysis was done by a market research firm or the magazine.

[oncallthrow]

Presumably by a journalist who doesn’t understand what market share is

[estimator7292]

Everybody else is telling you you're wrong and you're doubling down and insisting that respectable journals are morons who don't understand anything.

You should stop, reflect on this fact for a moment, then go pick up a goddamn book