operating expenses : 2013 versus 2012 versus ( percent of net sales ) 2013 2012 2011 .
in 2012 what was the percent of the voluntary early retirement incentive program to the increase in the pension and postretirement expense
pension and postretirement expense decreased $ 97 million in 2013 compared to 2012 , compared to an increase of $ 95 million for 2012 compared to 2011 . 2012 includes a $ 26 million charge related to the first-quarter 2012 voluntary early retirement incentive program ( discussed in note 10 ) . pension and postretirement expense is recorded in cost of sales ; selling , general and administrative expenses ( sg&a ) ; and research , development and related expenses ( r&d ) . refer to note 10 ( pension and postretirement plans ) for components of net periodic benefit cost and the assumptions used to determine net cost . cost of sales : cost of sales includes manufacturing , engineering and freight costs . cost of sales , measured as a percent of net sales , was 52.1 percent in 2013 , a decrease of 0.3 percentage points from 2012 . cost of sales as a percent of sales decreased due to the combination of selling price increases and raw material cost decreases , as selling prices rose 0.9 percent and raw material cost deflation was approximately 2 percent favorable year-on-year . in addition , lower pension and postretirement costs ( of which a portion impacts cost of sales ) , in addition to organic volume increases , decreased cost of sales as a percent of sales . these benefits were partially offset by the impact of 2012 acquisitions and lower factory utilization . cost of sales , measured as a percent of net sales , was 52.4 percent in 2012 , a decrease of 0.6 percentage points from 2011 . the net impact of selling price/raw material cost changes was the primary factor that decreased cost of sales as a percent of sales , as selling prices increased 1.4 percent and raw material costs decreased approximately 2 percent . this benefit was partially offset by higher pension and postretirement costs . selling , general and administrative expenses : selling , general and administrative expenses ( sg&a ) increased $ 282 million , or 4.6 percent , in 2013 when compared to 2012 . in 2013 , sg&a included strategic investments in business transformation , enabled by 3m 2019s global enterprise resource planning ( erp ) implementation , in addition to increases from acquired businesses that were largely not in 3m 2019s 2012 spending ( ceradyne , inc . and federal signal technologies ) , which were partially offset by lower pension and postretirement expense . sg&a , measured as a percent of sales , increased 0.3 percentage points to 20.7 percent in 2013 , compared to 20.4 percent in 2012 . sg&a decreased $ 68 million , or 1.1 percent , in 2012 when compared to 2011 . in addition to cost-control and other productivity efforts , 3m experienced some savings from its first-quarter 2012 voluntary early retirement incentive program and other restructuring actions . these benefits more than offset increases related to acquisitions , higher year-on-year pension and postretirement expense , and restructuring expenses . sg&a in 2012 included increases from acquired businesses which were not in 3m 2019s full-year 2011 base spending , primarily related to the 2011 acquisitions of winterthur technologie ag and the do-it-yourself and professional business of gpi group , in addition to sg&a spending related to the 2012 acquisitions of ceradyne , inc. , federal signal technologies group , and coderyte , inc . sg&a , measured as a percent of sales , was 20.4 percent in 2012 , a decrease of 0.4 percentage points when compared to 2011 . research , development and related expenses : research , development and related expenses ( r&d ) increased 4.9 percent in 2013 compared to 2012 and increased 4.1 percent in 2012 compared to 2011 , as 3m continued to support its key growth initiatives , including more r&d aimed at disruptive innovation . in 2013 , increases from acquired businesses that were largely not in 3m 2019s 2012 spending ( primarily ceradyne , inc . and federal signal technologies ) were partially offset by lower pension and postretirement expense . in 2012 , investments to support key growth initiatives , along with higher pension and postretirement expense , were partially .