How do marketing professionals figure out whether or not their investment in social media messaging has worked? The answer is, with difficulty.

According to a study by public relations company Edelman and the Marketing Institute of Ireland, nine in 10 marketers believe social media is important to their business, but a little more than half (51 per cent) say they cannot measure the return on their investment.

Not deterred by the measurement issues, three-quarters plan to increase their spending on social media this year, the survey of more than 100 marketers found.

When it comes to paid advertising on social media, Facebook was the most popular network, with 70 per cent indicated that they had used it in this way, compared to 40 per cent who had advertised on Twitter and 30 per cent who had spent money on LinkedIn.

“Whilst marketing teams are enthusiastic in their approach towards social, all too often they fail to embed the necessary structures to adequately measure success,” says Edelman’s head of digital, Darragh Rea.

Spending on paid advertising on social media will enjoy massive growth in 2015, Mr Rea predicts, while brands are likely to put a greater emphasis on interactivity and responsiveness on social media, rather than mere content publishing.

Contrary to popular belief, the study found that companies are handing over the management of their social media platforms to interns in only 5 per cent of cases. Even fewer – 4 per cent – had outsourced their posts and tweets to a PR agency. It’s all to pitch for.