(5) Measurement approach for fair value of share options granted during the period The weighted average fair value of share options granted during the period is determined using the binominal model based on the  following assumptions. 2013 2014 Share price at grant date 3,515 yen 5,430 yen Expected volatility (Note 1) 29.3% 29.6% Expected average period until the earliest exercisable date (Note 2) 4 years 3 years Expected dividend (Note 3) 125 yen/share 130 yen/share Risk-free rate (Note 4) 1.7% 1.7% (Note) 1. Estimated by taking into account the actual share prices for the past 20 years. 2. Estimated based on the service records and term of office. 3. Calculated based on the latest dividends paid. 4. Based on the yield of government bonds corresponding to the exercise period (20 years). The Group, excluding a part of foreign subsidiaries, offers  post-employment benefits such as defined benefit plans and  defined contribution plans. Among the defined benefit plans  offered, the defined benefit plan adopted in Japan is a major  one, accounting for approximately 70% of the total defined  benefit obligations. Defined benefit plans are exposed to actuarial risks. The  Astellas Corporate Pension Fund assigns staff with profes- sional knowledge and expertise about the composition of plan  asset to determine the asset mix ratio and manages risks by  monitoring on a quarterly basis. Among foreign subsidiaries, ones located in the United Kingdom,  Germany, the Netherlands, Ireland, and some other countries  offer defined benefit plans as post-employment benefits.  Among them, the defined benefit plan adopted in the Nether- lands is a major one. The Company and its domestic subsidiaries offer corporate  pension plans and retirement lump-sum payment plans as  defined benefit plans. The benefits of the defined benefit plan are determined  based on the base compensation calculated by accumulated  points earned by the time of retirement and promised rate of  return based on the yield of 10 year government bonds. Also,  the option of receiving benefits in the form of a pension is  available for plan participants with 15 years or more enrollments. Defined benefit plans are administered by the Astellas  Corporate Pension Fund. Directors of the pension fund are  jointly liable for damages to the fund due to their neglect of  duties about management of the funds. A benefit formula applied to the defined benefit plan of the  Netherlands is an average pay plan in which the amount of the  benefit calculated by multiplying the annual salary at a certain  ratio is accumulated. Defined benefit plans are managed by the Astellas pension  fund of the Netherlands. The board of the pension fund is  composed of employers and plan participants. In the Netherlands, it is required by local regulation to  maintain sufficient surplus in the pension fund and the fund is  monitored by the independent authority. If the amount of the  pension fund is lower than the minimum funding level, additional  contribution might be required. Contributions of the employer are made monthly and also  determined as 4.0% of standard salary, which is calculated  based on the estimate of the points granted during a year to  each participant. When the plan assets are lower than the  minimum funding standard at the end of the period, the  Financial Section 2. Defined benefit plans of overseas subsidiaries as post-employment benefits 1. Defined benefit plan adopted in Japan as post-employment benefit 28. retireMent Benefits employer will make additional contributions. Annual Report 2014 _  Astellas Pharma Inc.  133