The report, which surveyed 1,000 women over the last 12 months, is being published today ahead of International Women's Day tomorrow (8 March).
It suggests only 24 per cent of women in the UK feel adequately represented by brands. This is despite women accounting for 80 per cent of all purchases made globally, the report says.
Debbie Klein, CEO of Engine Europe and Asia-Pacific, said: "It is unacceptable that, in 2017, women still don't feel represented by advertisers. When 76 per cent of women don't see themselves in advertising, it's obvious something's gone wrong."
Almost 90 per cent of women think brands depict a stereotypical image of the modern British woman, which, according to the report, is particularly evident in advertising aimed at mothers.
Seventy per cent do not think brands understand their family lives, while 58 per cent think that the image of families presented by brands is "old-fashioned".
The report also shows that only 20 per cent of women think the automotive sector represents them accurately, while 60 per cent say they can't relate to beauty advertising.
According to the report, "persistent societal inequality" is to blame, with 93 per cent of those surveyed arguing that men and women are judged by different standards.
Over 90 per cent also say brands need to take more responsibility for how women are portrayed.
Klein said: "Of course, diagnosing the problem is far easier than finding a solution. There is no silver bullet, but there are some simple principles which can be applied and adapted."
She said that brands looking to engage the modern woman needed to look at all stages of the creative process to make sure that they are developing campaigns that are as targeted and relevant as possible.
"When speaking to a specific demographic, brands need to focus on eliminating unconscious bias, combatting traditional stereotypes, avoiding generalisations and drawing on these insights to create campaigns that reflect the varied experiences of the 21st century woman," Klein said.
Erminia Blackden, head of strategy at Engine-owned marketing firm Partners Andrews Aldridge, added that it was up to marketers to research the nuances and find more effective ways of communicating with women.
"Brands that get it right reap the benefits," she said.
The report is being launched at a panel discussion chaired by Klein. Panellists include Labour MP Stella Creasy, Stylist digital features editor Harriet Hall, and Kate Dale, head of brand and strategy at Sport England.
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