Figures revealed today show that almost half (48 percent) of online adverts do not reach the right people across France, Germany and Italy, and the U.K.
The statistics, from 's Digital Ad Ratings service, are likely to mean that billions of online marketing dollars are being wasted. Europe as a whole spent €36.4 billion ($37.9 billion) on digital advertising in 2015, according to the Interactive Advertising Bureau.
The consumer packaged goods sector fared the worst when it comes to ad impressions – or the number of times an online ad is seen by an audience – with only 42 percent of campaigns reaching the people they were aiming for.
Adverts for cars also fared poorly, with 45 percent reaching their intended audience, followed by those for computers and electronics, and shopping and retail (both with 49 percent). The best-performing sector is travel, where 65 percent of online ads reached the right people.
Nielsen's figures also show that advertising via desktop computers fared slightly better than those shown on mobile devices, reaching 52 percent of the intended audience versus 50 percent for mobile.
Campaigns aimed at people aged between 35 and 64 were more likely to reach the right audience, with 54 percent of ads reaching them, versus those aimed at younger people. Forty-four percent of online ad campaigns aimed at 18 to 34 year-olds were seen by them.
"Although 100 percent accuracy is likely to remain a pipe-dream, a school report on digital technology's ability to hit specific audiences might read 'could do better'," said Barney Farmer, Nielsen's marketing effectiveness director in the UK & Ireland.
But Farmer praised digital advertising's ability to reach people more effectively than other media. "However, in fairness it's more precise than traditional media and performance is improving all the time, particularly on mobile whose superiority in reaching narrower audiences reinforces its status as the most highly personal ad medium."
Consumer packaged goods – 58 percent
Automotive – 55 percent
Computers and electronics - 51 percent
Shopping and retail – 51 percent
Entertainment – 43 percent
Financial services – 43 percent
Business and consumer services – 40 percent
Travel – 35 percent
Figures are for France, Germany and Italy, and the U.K. and are for Q2, 2016, released by Nielsen on Thursday.
Clarification: This article has been updated since first published following clarification from Nielsen.