I once bought a book "How to be a Successfull Songwriter". Not Folk but it had a lot of useful tips.
One was to take a song you like (OK make it a folk song), write new words to it, then write a tune for the words.
What you end-up with is as derivative as your songwriting skills. Or as creative. What will leak through is the genre, a bit of style and the general format.

Now - one of the contributers/interviewees (one per chapter) was Neil Sedaka who just happened to have a TV programme about him recently. What he said was his first few offerings were "pretty awfull": BUT, he added, "the more you do it, the better you become". Also he said after his intial efforts were not up to the standard he demanded of himself (being at Juliard at the time) was that he surveyed every top ten song in the world (pinch of salt implied) and analysed them for common elements. Now so far so Folkie.
What he found was that they predominantly had a Girl's name in them, and were expressing male/female desire. His songs became commercial after that. And his record shows he deviated by following G.B. Shaw's maxim "The Golden Rule is that there are no golden rules".
So the survey has to reflect the genre and the results will throw-up different commonalities but the methodology is sound. It is market research on the "consumer" by one remove - what they like, is what they consume.