With the co-operation of Clear Channel's Adshel, Portland ran a six-sheet campaign for a fictional advertiser in two Yorkshire towns - one with a high ethnic population and one with a high white population.
The research revealed that campaigns that use imagery that resonates strongly with its respective audience are the most effective. For example, a campaign that featured an image associated with the Black Caribbean community recorded a 50 per cent higher unprompted recall among this ethnic group than across all others.
The research also found that ethnic minorities tended to be more inclined to take advertising at face value than white communities, who were slightly more cynical. This could be because the demographic profile of the ethnic community is younger than that of the indigenous population.
Ethnic communities also showed greater awareness of poster advertising than their white counterparts and were also more inclined than white people to say that posters were informative.
Andrew Atherton, the research and marketing director of Portland Outdoor and a director of ForeSite, said: "With the growth of outdoor as a medium, it's vital that the industry keeps pace with major societal changes, such as the growth and development of ethnic audiences in the UK and the effectiveness of outdoor in addressing them.
"From this exploratory study, it is clear that outdoor media has a significant role to play, and that advertisers must tailor their imagery precisely to their audience."