Note 10. Warrant Liability

Our outstanding warrants are recorded as liabilities at their estimated fair value at the date of issuance, with the subsequent changes in estimated fair value recorded in other income (expense) in the Company’s statement of operations in each subsequent quarterly period. The change in the estimated fair value of our warrant liability for the years ended December 31, 2015 and 2014 resulted in non-cash income of approximately $2.3 million and non-cash income of approximately $1.2 million, respectively. The Company utilizes the Monte Carlo simulation valuation method to value the liability classified warrants.

The estimated fair value of these warrants is determined using Level 3 inputs. Inherent in the Monte Carlo valuation model are assumptions related to expected stock-price volatility, expected life, risk-free interest rate and dividend yield. The Company estimates the volatility of its common stock based on historical volatility that matches the expected remaining life of the warrants. The risk-free interest rate is based on the U.S. Treasury zero-coupon yield curve on the grant date for a maturity similar to the expected remaining life of the warrants. The expected life of the warrants is assumed to be equivalent to their remaining contractual term. The dividend rate is based on the historical rate, which the Company anticipates to remain at zero.

The following table summarizes the calculated aggregate fair values, along with the assumptions utilized in each calculation:

The nature of the warrant liability is such (i.e., the warrant holders receive more value when the Company’s stock price is higher) that increases in the Company’s stock price during the period result in losses on the Company’s income statement while decreases in the Company’s stock price result in the Company recording income.