2010 10-K: Part II 2010 vs. 2009 2009 vs. 2008 74 While operating expense generally increased in 2010, we recorded  $9.5 million of operating expense in 2009 related to adjusting the  treatment of some incentive stock options and penalties related to  the timing of deposits for taxes withheld on stock-option exercises  that did not recur in 2010. In addition, the recorded expense related  to increasing liabilities for vacant office declined by $2.2 million  compared with the amount recorded in 2009. Intangible amortization expense increased $5.9 million compared  with 2009, reflecting additional amortization expense from recent acquisitions. The positive impact of these cost reductions was partially offset by  incremental costs from acquisitions. We completed six acquisitions  in 2009 and six in 2008. Because of the timing of these acquisitions,  our 2009 results include operating expense that did not exist in  2008. Headcount and salary expense increased year over year, partly  because of incremental employees added through acquisitions. We  had approximately 2,605 employees worldwide as of December 31,  2009, a 9.7% increase from 2,375 employees as of December 31,  2008. We added approximately 170 employees through acquisitions  over the 12 months ending December 31, 2009. The remainder of  the increase in headcount reflects continued hiring for our develop- ment center in China. Higher incentive compensation and employee benefit costs repre- sented approximately 40% of the overall operating expense increase  in 2010. In early 2010, we began phasing in some of the benefits  and other compensation-related expense we reduced in 2009. As  a result, bonus expense increased $16.3 million, or 77.6%, in 2010.  Sales commissions increased $7.8 million in 2010, reflecting  improved sales activity compared with 2009 as well as a change to  one of our commission plans. Matching contributions to our 401(k)  plan in the United States increased $3.5 million in 2010 because  we partially reinstated this employee benefit in 2010. In addition,  healthcare benefit costs rose $2.8 million in 2010. Operating expense  in 2010 also included $2.0 million related to a previously announced  separation agreement between Morningstar and the former head  of Morningstar Associates. We also suspended matching contributions to our 401(k) program  in the United States, which reduced operating expense by about  $6.6 million. In addition, we reduced discretionary spending on travel,  advertising, and marketing. Travel costs were about $4.5 million  lower in 2009. Advertising and marketing costs declined by $4.3  million in 2009. In addition, we discontinued three publications  previously published, which contributed to lower marketing expense  in 2009. Our consolidated operating expense decreased $9.3 million, or 2.5%,  in 2009 compared with 2008. To better align operating expense with  revenue in a challenging business environment, we took a number  of steps to reduce costs beginning in 2008, with the largest cutbacks  effective January 1, 2009. We changed our bonus plan in 2009 to  reduce bonus expense, our single largest discretionary cost. As a  result, bonus expense was down about $28.9 million in 2009. The  significant reduction in bonus expense also reflects a slowdown in  our financial performance in 2009 compared with 2008. Higher salary expense represented slightly more than one-third of  the total operating expense increase, reflecting higher headcount  from acquisitions and filling open positions, as well as salary  increases made in July 2010. We had approximately 3,225 employ- ees worldwide as of December 31, 2010, a 23.8% increase from  2,605 as of December 31, 2009. We added about 125 employees  through acquisitions over the 12 months ending December 31, 2010.  The remainder of the increase in headcount mainly reflects contin- ued hiring for our development centers in China and India. In 2010, our consolidated operating expense increased $80.0 million,  or 22.6%. We completed seven acquisitions in 2010 and six in 2009.  Because of the timing of these acquisitions, our results include  operating expense that did not exist in the same periods last year.  Incremental operating expense from acquired businesses repre- sented more than half of the operating expense increase. In 2010,  we restored some compensation and employee benefits after reduc- ing them in 2009, contributing to the operating expense increase. Operating expense as a percentage of revenue increased 4.2 per- centage points in 2010, as the 22.6% increase in operating expense  outpaced the 15.9% increase in revenue.