Read the italicised extract from Man Utd's Report and Accounts. They pay for and value information like this because it drives their commercial operation. You can question the underlying data, or you may find it boring, but it's important.
"References to our “1.1 billion fans and followers” are based on the Survey commissioned by us, conducted by Kantar Media (Media Division of Kantar and division of WPP plc) (“Kantar”) in 2019, and paid for by us. As in the Survey conducted by Kantar, we defined the term “fans” as those individuals who answered survey questions, unprompted, with the answer that Manchester United was their favorite football team in the world and the term “followers” as those individuals who answered survey questions, unprompted, with the answer that Manchester United is a football team that they proactively follow in addition to their favorite football team. For example, we directed Kantar to include in the definition of “follower” a respondent who watched live Manchester United matches, followed highlights coverage or read or talked about Manchester United regularly. The Survey was conducted during the first six months of 2019 and included over 54,000 respondents across 39 countries. It repeated a similar 2011 survey, also conducted by Kantar, to assess comparability of approach, methodology and results. The Survey included questions on: • demographics, age, gender and socio-economic background; • viewership of Manchester United matches, social media following and engagement; • relationship, awareness and attitudes to commercial partners; and • interest in Manchester United products, including merchandise. The Survey indicated that Manchester United has 1.1 billion combined fans and followers worldwide, comprised of 467 million fans and 635 million followers (compared to 277 million and 382 million, respectively, in 2011)... "
