When we think about the kinds of teachers we hope our children have, we realize that it's impossible to capture everything in a single metric.

WSJ: Bill and Melinda Gates on Teacher Evaluation

Unlike other company rankings that use a single metric (generally revenue), Forbes works diligently to take a holistic gauge of the growth prospects for young, privately held firms.

FORBES: Last Chance To Nominate For Forbes' List Of America's Most Promising Companies

Because interactions as a single metric is only the surface.

FORBES: SpongeBob SquarePants vs. The X Factor: A Social TV Throwdown In Infographics

Ranking companies on a single metric, like sales, can be misleading, which is why Forbes uses a composite ranking, giving equal weight to sales, profits, assets and market value.

FORBES: VW Is Already The World's Leading Automaker

Yet not everyone is looking at a single metric.

FORBES: Market Scan