I wonder how many people left that blank on the basis that it's no-one's business but their own and therefore were counted as atheists?
An interesting point, although exploring the page on that link just now, I noticed that there had also been a 'religion not stated' category on the census form, so presumably the 'mind your own business' group would appear there?
If you look at 'health' on that DataShine page, you'll see that the inhabitants of North Marple enjoy much better health than those of South Marple. It must be the bracing breezes in these northern latitudes.
Or maybe prayer does work after all.