@satsuma @jdonoghue @CrypticMirror Very few people have much of a sense of what might be happening in places beyond their local area. If you're a regular churchgoer, you might be very aware of trends in numbers in your own congregation, might be vaguely aware of what numbers are like in a few other churches nearby or which your congregation has links to, but would likely have little idea of what trends might be happening nationally. For this, you need national level data gathering organisations, like YouGov, which is where fault seems to lie in this case.

The only ones within the church who might have access to national-level figures to question the data would be national denominational bodies, but even then, they would only have access to (often pretty patchy/poor quality) data from their own denomination, rather than across denominations (lots of silo-ing happens in churches, with relatively little co-ordination between denominational bodies).

And then there are cross-denominational parachurch organisations that might also have a bit of a sense of what is happening more broadly, though without much granular data, who might have had anecdotal reasons to question the data. And in this case, one of the most relevant bodies did precisely that.