pre_text: edwards lifesciences corporation notes to consolidated financial statements ( continued ) 12 . common stock ( continued ) the company also maintains the nonemployee directors stock incentive compensation program ( the 2018 2018nonemployee directors program 2019 2019 ) . under the nonemployee directors program , each nonemployee director may receive annually up to 10000 stock options or 4000 restricted stock units of the company 2019s common stock , or a combination thereof , provided that in no event may the total value of the combined annual award exceed $ 0.2 million . additionally , each nonemployee director may elect to receive all or a portion of the annual cash retainer to which the director is otherwise entitled through the issuance of stock options or restricted stock units . each option and restricted stock unit award granted in 2011 or prior generally vests in three equal annual installments . each option and restricted stock unit award granted after 2011 generally vests after one year . upon a director 2019s initial election to the board , the director receives an initial grant of restricted stock units equal to a fair market value on grant date of $ 0.2 million , not to exceed 10000 shares . these grants vest over three years from the date of grant . under the nonemployee directors program , an aggregate of 1.4 million shares of the company 2019s common stock has been authorized for issuance . the company has an employee stock purchase plan for united states employees and a plan for international employees ( collectively 2018 2018espp 2019 2019 ) . under the espp , eligible employees may purchase shares of the company 2019s common stock at 85% ( 85 % ) of the lower of the fair market value of edwards lifesciences common stock on the effective date of subscription or the date of purchase . under the espp , employees can authorize the company to withhold up to 12% ( 12 % ) of their compensation for common stock purchases , subject to certain limitations . the espp is available to all active employees of the company paid from the united states payroll and to eligible employees of the company outside the united states to the extent permitted by local law . the espp for united states employees is qualified under section 423 of the internal revenue code . the number of shares of common stock authorized for issuance under the espp was 6.6 million shares . the fair value of each option award and employee stock purchase subscription is estimated on the date of grant using the black-scholes option valuation model that uses the assumptions noted in the following tables . the risk-free interest rate is estimated using the u.s . treasury yield curve and is based on the expected term of the award . expected volatility is estimated based on a blend of the weighted-average of the historical volatility of edwards 2019 stock and the implied volatility from traded options on edwards 2019 stock . the expected term of awards granted is estimated from the vesting period of the award , as well as historical exercise behavior , and represents the period of time that awards granted are expected to be outstanding . the company uses historical data to estimate forfeitures and has estimated an annual forfeiture rate of 5.1% ( 5.1 % ) . the black-scholes option pricing model was used with the following weighted-average assumptions for options granted during the following periods : option awards .
post_text: .
table: 2013 2012 2011
table: Average risk-free interest rate 0.8% 0.7% 1.7%
table: Expected dividend yield None None None
table: Expected volatility 31% 31% 27%
table: Expected life (years) 4.6 4.6 4.5
table: Fair value, per share $19.47 $23.93 $22.78
question: Analyse this data from a financial earnings document. what is the percentage change in the fair value per share between 2011 and 2012?