Introspectively I always felt that music helps me get into a focused state but I always wondered whether it has any effects. Over the course of May 2014 I collected some data on my own writing performance in different circumstances when I had a lot of written work to complete (a bit over100 hours spent on writing in that month).

Every 30min I took a break and gave a 1-10 rating of the quality of the work I had completed in that period, and brief notes about anything else that might be notable. I admit that self-rating is rather arbitrary but simply word count wouldn't suffice as I was also editing, consulting sources and other tasks related to writing at various times. And of course these results may not generalise to anyone besides myself (and indeed for my own purposes I should do a replication next time I have a huge writing crunch). Mean self-rating of "quality":

* Office, no music: ___ 5.4 (10.5hr)
* Office, instrumental: 5.8 (21.5hr)
* Office, vocal: ______ 5.9 (20hr)
* Library, no music ___ 4.2 (5.5hr)
* Home, instrumental __ 5.3 (23hr)
* Home, vocal _________ 5.5 (21.5hr)

The mean ratings above conceal a lot of variability; the only reliable effect (Wilcoxon-Mann-Whitney test) was that the university library is a horrible place for me to get anything done (No music: Library < Home and Library < Office). No surprise there - as in my undergraduate studies the library seems mostly to be a place people go to avoid doing work. The apparently lower mean in "Office, no music" was driven by a couple of outliers related to distraction by other people.

main musical styles (not possible to analyse due to variability): old thrash metal, new doom metal, psychedelic folk music, rockabilly, bluegrass, shoegaze, bebop/hard bop, J-pop, person with guitar.

final note: I do not tend to notice the details of lyrics unless i am paying very close attention to the music, even for highly lyrical music I still mostly focus on the instrumental parts.