in economics; Market share change relative to market growth

Hi all
I am not professional neither in economics nor in statistics, and I was wondering if you could help me:

I am working on a project that simulates a systems that tells to companies if they are doing good or bad considering their marketing share.

Lets say we are in the fax industry, and there are A,B,C,D...Z brands in this Industry.
Lets say that you are Brand D. last year you sold in 100k$ and this year you sold in 90k$. so you lost 10% of your sales, which is bad.
from the other hand, all the fax industry is declining, and the whole market reduced in 40%.
So from this perspective, you lost only 10% while the general market lost 40%. so from this view point, you are doing great.

Is there a statistical metric that measures this kind of changes? Is there a name for it. what is the best way to measure it?

Thank you in advance


No cake for spunky
Good and bad is a relative concept which requires judgement on the part of the organizational leadership. Some might stress maximizing income, some minimizing risk, some keep labor cost down etc. So you have to access this answer tied to what priorities they have - which almost certainly will be different among firms.

If you create a list that ranks the firms on given criteria this would seem to get at what you want (although that is not a statistical test). If you rank them on multiple criteria at one time you would have to weight and combine the criteria to do so. If you want a statistical test (sort of) you can calculate which firms are statistical outliers on given criteria for example with a Tukey boxplot.

Another approach, again not formally statistics, is linear programing which show how to maximize gain (or minimize risk) given certain goals and specific resources.