In case you had any doubt that it would, the Forbes Most Innovative Growth Companies List includes a pair of the giants in the 3D printing business.

The list for 2014 includes 3D Systems Corporation (ranked 13th of 100) and Stratasys was 32nd.

What might be surprising is that there weren't more 3D printing companies making the list.

The Forbes list wasn't created out of whole cloth, but instead uses a formula to calculate which companies should be included.

Christensen's disruption graph

Clayton Christensen

Primarily the work of Harvard Business School Professor and researcher Clayton Christensen, the Forbes list is based on metrics collected to determine how business innovators operate. Calling the core metrics the Innovation Premium, Christensen and his fellow researchers, Jeff Dyer and Hal Gregersen, have also written a book on the topic; The Innovators DNA.

Christensen, the Kim B. Clark Professor of Business Administration at the Harvard Business School, teaches a popular elective class called Building and Sustaining a Successful Enterprise. As one of the world's top experts on innovation and growth, his concepts have been adopted by industrial and business organizations around the world. He's the author of some nine books including The Innovator's Dilemma.

According to Forbes, the ordering of the list is based on "investors' ability to identify firms they expect to be innovative now and in the future." The application of the Innovation Premium results in a projection of a company's income from existing businesses, plus anticipated growth from those businesses and the net present value (NPV) of cash flow. The study also uses a "fade algorithm" using data from 45,000 firms and more than 500,000 data points.

To make the list, firms are required to have seven years of available public financial data and to be under $10 billion in market cap.