edwards lifesciences corporation notes to consolidated financial statements ( continued ) 13 . 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 20000 stock options or 8000 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 . 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 . 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 shares . each option received as a deferral of the cash retainer immediately vests on the grant date , and each restricted share award vests after one year . upon a director 2019s initial election to the board , the director receives an initial grant of stock options 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 6.9 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 lifesciences 2019 stock and the implied volatility from traded options on edwards lifesciences 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 5.4% ( 5.4 % ) . the black-scholes option pricing model was used with the following weighted-average assumptions for options granted during the following periods : option awards .

 | 2014 | 2013 | 2012
----------|----------|----------|----------
average risk-free interest rate | 1.5% ( 1.5 % ) | 0.8% ( 0.8 % ) | 0.7% ( 0.7 % )
expected dividend yield | none | none | none
expected volatility | 31% ( 31 % ) | 31% ( 31 % ) | 31% ( 31 % )
expected life ( years ) | 4.6 | 4.6 | 4.6
fair value per share | $ 23.50 | $ 19.47 | $ 23.93

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Question: what is the expected change according to the model in the fair value per share between 2013 and 2014?
Program: subtract(23.50, 19.47)
Answer: 4.03