Originally posted by: silverpig
Originally posted by: LegendKiller
Originally posted by: silverpig
The DOW is at 12300 today.
12300 what?
http://en.wikipedia.org/wiki/D...nes_Industrial_Average
Ahh okay, so it seems like there exists a list of companies which make up the DJIA. The number comes from summing the stock prices of those companies, then dividing by some number.
(I'm not a finance guy)
Its just an index that cannot be compared to other indecies. The index is a weighted average of the market cap of the companies. If the average goes up, the index goes up, if the average goes down, the index goes down.
Say, I make "Martin's Index" which will be structured like this: On March 3rd, the index will start at 1000 points and will be made up of 50% Google, 25% MS and 25% RIM. Then every day I track how much the market cap changes and that gets reflected in my points. So on March 3rd at 9am it will be 1000, but during trading day, GOOG goes up 5%, MSFT goes down 10% and RIMM goes up 10%. When you sum that up and apply the weights, Martin's index will be up 2.5%, which means that it'll be at 1025 (25% of the index (MSFT) went down 10%, 25% of the index (RIMM) went up 10% and 50% of the index (GOOG) went up 5%).
Each index (SP500, DOW, TSX) has different weights and is composed of different companies. For example, the DOW are picked to be a representative sample of the economy, while the SP500 is simply the 500 largest companies. The composition of the indecies also changes every now and then. The points themselves are meaningless - anybody can make their own index and can make it start at any number of points. They only make sense when compared to themselves (DOW being 300 points means it lost ~2.5%)
Anyway, that's generally how it works (AFAIK). I recommend you pick up
this book. Its an excellent (and very readable) intro to how markets work.