An analysis of the ARC database indicates that campaigns with a roughly equal mix of online advertising (mainly paid search, social media in-feed and youtube) and 'traditional' advertising (mainly TV) tend to deliver bigger revenue uplifts compared to campaigns with higher or lower proportions of online spend.
This further supports Binet and Field's conclusions in 'The Long and Short of it'. They found that the optimum mix of 'Brand Activation' and 'Brand Building' advertising spend was 40:60. Although Brand Activation and Brand Building do not correspond perfectly with online and offline advertising, there is still a very close relationship between them which means that marketers can be increasingly confident that a roughly equal balance between online/activation advertising and traditional/brand building advertising is the way to go.
To obtain the full report, search for 'Feedback from the front lines: New data on effectiveness outside award winners, Dr Grace Kite and Paula Gonzales, October 2021'.