Analysis tool CampaignDeus undertook a survey of 4,500 UK influencers, studying 700,000 individual posts from their Instagram accounts in the first half of 2018.
UK-based influencers with a very low proportion of their audience based in the UK, unexplained leaps in follower counts and unusually low engagement rates were identified as likely to have artificially expanded their follower count - the study says 12% of the accounts did so in the period.
The study also shows that 34% of branded posts by these influencers are for fashion and style brands, followed by 23% for beauty brands and 16% for food and drink.
It also tracks the sectors with the biggest growth in branded posts over the period:
- Fitness: 7.6%
- Travel: 4.4%
- Parenting 3.5%
- Beauty 2.9%
- Food & drink 1.7%
- Fashion & style 1.4%
- Home & garden 1.3%
- Health 0.4%
The automotive sector sees the biggest drop - 4%.
The study also shows that engagement rates are on average 11% lower on sponsored posts versus organic posts - a figure rising to 27% in beauty. Parenting is the only sector where this engagement drop-off is not present.
Finally, it finds that influencers with fewer than 100,000 followers achieve on average 60% higher engagement than those with six-figure fandoms.
CampaignDeus chief executive Muhsen Syed said: "To optimise their influencer marketing spend, brands need to stop fruitlessly searching for a magic return on investment number, which doesn’t accurately exist.
"The focus should be on building a systems-based approach to influencer marketing measurement, which places benchmarking at its core, so brands can easily compare their performance against their competitors and the broader market."
A version of this article was first published by PRWeek