the estimated fair value of the reporting unit. The estimated fair value of a reporting unit is determined using earnings for the reporting unit multiplied by a price/earnings ratio for comparable industry groups, or by using a discounted cash flow analysis. 3M typically uses the price/earnings ratio approach for stable and growing businesses that have a long history and track record of generating positive operating income and cash flows. 3M uses the discounted cash flow approach for start-up, loss position and declining businesses, but also uses discounted cash flow as an additional tool for businesses that may be growing at a slower rate than planned due to economic or other conditions.

 

As discussed in Note 3 to the Consolidated Financial Statements, effective in the first quarter of 2012, 3M made certain product moves across divisions within its business segments, but none were across business segments. For any product moves that resulted in reporting unit changes, the Company applied the relative fair value method to determine the impact to reporting units. During the first quarter of 2012, the Company completed its assessment of any potential goodwill impairment for reporting units impacted by this new structure and determined that no impairment existed. The discussion that follows relates to the separate fourth quarter 2012 annual impairment test and is in the context of the segment structure that existed at that time.

 

As of September 30, 2012, 3M had 36 primary reporting units, with ten reporting units accounting for approximately 77 percent of the goodwill. These ten reporting units were comprised of the following divisions: 3M Purification Inc., Occupational Health and Environmental Safety, Optical Systems, Security Systems, Infection Prevention, 3M ESPE, Industrial Adhesives and Tapes, Communication Markets, Health Information Systems, and Abrasive Systems. The fair values for all these significant reporting units were in excess of carrying value by approximately 50 percent or more.

 

In 2012, 3M primarily used an industry price-earnings ratio approach, but also used a discounted cash flows approach for certain reporting units, to determine fair values. Where applicable, 3M used a weighted-average discounted cash flow analysis for certain divisions, using projected cash flows that were weighted based on different sales growth and terminal value assumptions, among other factors. The weighting was based on management’s estimates of the likelihood of each scenario occurring.

 

Based on fourth-quarter 2012 testing, 3M’s estimated fair value when valuing each reporting unit individually would aggregate to approximately $77 billion, implying a control premium of 21 percent when compared to 3M’s market value of approximately $64 billion at both September 30, 2012 and December 31, 2012. The control premium is defined as the sum of the individual reporting units estimated market values compared to 3M’s total Company estimated fair value, with the sum of the individual values typically being larger than the value for the total Company. 3M’s market value at both September 30, 2012 and December 31, 2012 was significantly in excess