I've read a number of the Westphalian prefects' reports on l'esprit publique, and those are fascinating, but I can't tell what, if any, method the prefect used to reach his conclusions. In most cases he appears to be offering a handful of anecdotes and then generalizing, and there's no way to know whether he's not fabricating in any event. Given that prefects were sometimes sloppy with other tasks such as counting population and property for tax purposes (suspiciously round numbers abound on these reports, unchanging year after year), we can't really know if those reports on "opinion" are worth much.