It looks like Wall Street’s chaos might just affect online advertising more than some thought a few days ago. Just in time for the financial markets’ meltdown this week, Nielsen Online finds a 27 percent decline in display ad spending by financial services companies drove a 6 percent year-over-year decrease in overall display dollars in the first half of 2008. The number of display impressions decreased by 9 percent during the same period. When paid search figures from other sources is factored in, along with the projected growth of online video advertising, Nielsen estimated that overall online ad spending gained about 11 percent during the first half of 2008. Overall, ad spend across all media slipped 1.4 percent in H108, Nielsen says. The financial services industry – consistently among the top online spending segments, Nielsen says – showed estimated expenditures of $1.1 billion during the first two quarters compared to $1.5 billion during the same period in 2007. Although historically a smaller advertising segment, the public services industry also contributed to the decrease, declining by 38 percent.