From a reader:

Dear Mr Derbyshire—Thank you for your warm appreciation of Saturday Night Fever. I’ve never seen it; but I’ll put on the Netflix queue. Since you ask what disco is good for, I’ll tell you. My sister studied deaf ed at Flagler College in Florida, during the disco years. She and her fellow students used to go disco-dancing — both those who could hear, and the deaf. The deaf students *loved* disco — they could feel the bass and so dance in time with the music. Thereby proving the universality of dancing. Not exactly a sterling endorsement — ‘Disco: The Favorite Music of the Deaf!’ — but since you asked, there it is.