The research, from Nielsen’s Digital Ad Ratings service, looked at more than 44,000 campaigns across 17 countries and found that the accuracy of ad targeting varied considerably by sector.

Travel ads were the most likely to reach their intended audience in the UK – doing so 66% of the time – followed by entertainment at 64%. The least well targeted were FMCG ( 40%) and retail ( 42%).

The hardest to reach demographic online were the 25- to 44-year-olds. Campaigns aimed at this group reached them 38% of the time, compared with 44% of campaigns targeting 18- to 34-year-olds and 58% for 35- to 64-year-olds.

Barney Farmer, Nielsen’s marketing effectiveness director in the UK & Ireland, said: “Although 100% 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’.

“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.”