>View from the product side of the fence:
>On the other hand, when products reach a >different percentage of the people, the >percentages should add up to 100.
no they shouldn't. each product should have a portion of 100% of the market that they reach. If each person was only able to ever be exposed to one product then you're right, but since we are exposed to more than one... Each product could not have more than 100% market reach, that would be illogical, but they can all have 99.99% if they like.. if they're all really good at reaching us.
Market share is the metric that asks the question, which product do you prefer and use, and since we can only prefer 1 product over all of the others, the market becomes the 1 or whole, and each product can have a portion (or share) of that. All of *those* numbers must add up to 100%, or the whole market.
So I think what you're thinking is
when products *are preferred* by different percentages of the people, those percentages should add up to 100% - reach is a very different thing, and presents it's own value for consideration. Not to say market share wouldn't be a more valuable or immediately useful measure, but it's not as easy to come across or calculate.
yu zimmi?
OK the math is a little old school around here i see, like someone just posted that they get 300% more traffic from one source than another, but what they mean to say is they get 3 times as much. 300% doesn't exist, as 282% doesn't exist. of course thats a very old and not very search engine related argument.
and i thought math was supposed to clarify things.. ugg.