188 NOTES TO THE CONSOLIDATED FINANCIAL STATEMENTS OF AEGON N.V.  NOTE 25 SENSITIVITY OF ASSUMED MEDICAL COST TREND  RATES:  Assumed medical cost trend rates have an effect on the  amounts reported for the health care plans. A one-percentage  change in assumed medical cost trend rates would have the  following effects: An experience adjustment on plan liabilities is the difference  between the actuarial assumptions underlying the scheme and  the actual experience during the period. This excludes the  effect of changes in the actuarial assumptions that would also  qualify as actuarial gains and losses. Experience adjustments  on plan assets are the difference between expected and actual  return on assets. Defined benefit plans are mainly operated by AEGON USA,  AEGON The Netherlands and AEGON UK. The following sections  contain a general description of the plans in each of these  subsidiaries, a summary of the principal actuarial assumptions  applied in determining the value of defined benefit plans and a  description of the basis used to determine the overall expected  rate of return on plan assets.  AEGON USA has defined benefit plans covering substantially all  its employees that are qualified under the Internal Revenue  Service Code. The benefits are based on years of service and  AEGON USA also sponsors supplemental retirement plans to  provide senior management with benefits in excess of normal  pension benefits. These plans are unfunded and non-qualified  under the Internal Revenue Service Code. The unfunded  amount related to these plans, for which a liability has been  recorded, is EUR 184 million (2009: EUR 192 million). the employee’s eligible annual compensation. The defined  benefit plans were unfunded by EUR 171 million at December 31,  2010 (2009: EUR 113 million unfunded).  AEGON USA  Estimated future benefi ts: Pension  benefi ts  Other  benefi ts  Total 2011 237 18 255 2012 248 17 265 2013 244 20 264 2014 250 21 271 2015 254 22 276 2016-2020 1,346 120 1,466 Experience adjustments arising on: 2010 2009 2008 2007 2006 Plan liabilities 59 (11) (3) (37) (76) Plan assets 175 241 (882) 64 112 2010 2009 + 1% – 1% + 1% – 1% Aggregate of current service cost and interest cost components of net periodic  post-employment medical costs 2 (1) 2 (1) Accumulated post-employment benefit obligation for medical cost 18 (16) 14 (13) Best estimate of contributions expected for the next  annual period 104