Harvard Business Review: What businesses get wrong about digital advertising 15 Mar, 2021 12:52 AM 6 minutes to read Harvard Business Review By: Sinan Aral The effectiveness of digital ads is wildly oversold. A large-scale study of ads on eBay found that brand search ad effectiveness was overestimated by up to 4,100 per cent. A similar analysis of Facebook ads threw up a number of 4,000 per cent. For all the data we have, it seems like companies still don't have an answer to a question attributed to the famous 19th-century retailer John Wanamaker: Which half of my company's advertising budget is wasted? It should be possible to answer this question, though. Because what's getting in the way is not a lack of information — the problem Wanamaker faced — but rather a fundamental confusion between the phenomena of correlation and causation.