discount rate 2014the assumed discount rate is used to determine the current retirement related benefit plan expense and obligations , and represents the interest rate that is used to determine the present value of future cash flows currently expected to be required to effectively settle a plan 2019s benefit obligations .
the discount rate assumption is determined for each plan by constructing a portfolio of high quality bonds with cash flows that match the estimated outflows for future benefit payments to determine a single equivalent discount rate .
benefit payments are not only contingent on the terms of a plan , but also on the underlying participant demographics , including current age , and assumed mortality .
we use only bonds that are denominated in u.s .
dollars , rated aa or better by two of three nationally recognized statistical rating agencies , have a minimum outstanding issue of $ 50 million as of the measurement date , and are not callable , convertible , or index linked .
since bond yields are generally unavailable beyond 30 years , we assume those rates will remain constant beyond that point .
taking into consideration the factors noted above , our weighted average discount rate for pensions was 5.23% ( 5.23 % ) and 5.84% ( 5.84 % ) , as of december 31 , 2011 and 2010 , respectively .
our weighted average discount rate for other postretirement benefits was 4.94% ( 4.94 % ) and 5.58% ( 5.58 % ) as of december 31 , 2011 and 2010 , respectively .
expected long-term rate of return 2014the expected long-term rate of return on assets is used to calculate net periodic expense , and is based on such factors as historical returns , targeted asset allocations , investment policy , duration , expected future long-term performance of individual asset classes , inflation trends , portfolio volatility , and risk management strategies .
while studies are helpful in understanding current trends and performance , the assumption is based more on longer term and prospective views .
in order to reflect expected lower future market returns , we have reduced the expected long-term rate of return assumption from 8.50% ( 8.50 % ) , used to record 2011 expense , to 8.00% ( 8.00 % ) for 2012 .
the decrease in the expected return on assets assumption is primarily related to lower bond yields and updated return assumptions for equities .
unless plan assets and benefit obligations are subject to remeasurement during the year , the expected return on pension assets is based on the fair value of plan assets at the beginning of the year .
an increase or decrease of 25 basis points in the discount rate and the expected long-term rate of return assumptions would have had the following approximate impacts on pensions : ( $ in millions ) increase ( decrease ) in 2012 expense increase ( decrease ) in december 31 , 2011 obligations .

($ in millions)
Increase (Decrease) in 2012 Expense
Increase (Decrease) in December 31, 2011 Obligations
25 basis point decrease in discount rate
$18
$146
25 basis point increase in discount rate
(17)
(154)
25 basis point decrease in expected return on assets
8
n.a.
25 basis point increase in expected return on assets
(8)
n.a.

differences arising from actual experience or changes in assumptions might materially affect retirement related benefit plan obligations and the funded status .
actuarial gains and losses arising from differences from actual experience or changes in assumptions are deferred in accumulated other comprehensive income .
this unrecognized amount is amortized to the extent it exceeds 10% ( 10 % ) of the greater of the plan 2019s benefit obligation or plan assets .
the amortization period for actuarial gains and losses is the estimated average remaining service life of the plan participants , which is approximately 10 years .
cas expense 2014in addition to providing the methodology for calculating retirement related benefit plan costs , cas also prescribes the method for assigning those costs to specific periods .
while the ultimate liability for such costs under fas and cas is similar , the pattern of cost recognition is different .
the key drivers of cas pension expense include the funded status and the method used to calculate cas reimbursement for each of our plans as well as our expected long-term rate of return on assets assumption .
unlike fas , cas requires the discount rate to be consistent with the expected long-term rate of return on assets assumption , which changes infrequently given its long-term nature .
as a result , changes in bond or other interest rates generally do not impact cas .
in addition , unlike under fas , we can only allocate pension costs for a plan under cas until such plan is fully funded as determined under erisa requirements .
other fas and cas considerations 2014we update our estimates of future fas and cas costs at least annually based on factors such as calendar year actual plan asset returns , final census data from the end of the prior year , and other actual and projected experience .
a key driver of the difference between fas and cas expense ( and consequently , the fas/cas adjustment ) is the pattern of earnings and expense recognition for gains and losses that arise when our asset and liability experiences differ from our assumptions under each set of requirements .
under fas , our net gains and losses exceeding the 10% ( 10 % ) corridor are amortized .

Question: Analyse this data from a financial earnings document. what is the percentage change in the weighted average discount rate for pensions from 2010 to 2011?
Choices:
-104.45205
-0.10445
-9.57377
33.41781
1.89555
Correct choice index: 1