pre_text: ASSUMPTIONS USED IN STOCK OPTION PRICING MODEL The fair value of options granted was determined using a variation of a binomial option pricing model that takes into account factors specific to the share incentive plans, such as the vesting period. The following table shows the principal assumptions used in the valuation. Expected dividend growth is commensurate with BCE’s dividend growth strategy. Expected volatility is based on the historical volatility of BCE’s share price. The risk-free rate used is equal to the yield available on Government of Canada bonds at the date of grant with a term equal to the expected life of the options
table: 2019 2018
table: Weighted average fair value per option granted $2.34 $2.13
table: Weighted average share price $58 $57
table: Weighted average exercise price $58 $56
table: Expected dividend growth 5% 5%
table: Expected volatility 14% 12%
table: Risk-free interest rate 2% 2%
table: Expected life (years) 4 4
question: Analyse this data from a financial earnings document. What is the average expected life over 2018 and 2019?