From the book:
“We sort of tricked Jane into making this sweater. She already knew how to knit and purl when we met her, but she wasn’t confident in her skills to attempt an actual garment…so we started her on a scarf that was knit in stockinette stitch and wide enough that it wouldn’t matter if the scarf rolled in a bit at the edges…Imagine her surprise when we did some minor adjusting and changed the scarf…into a sweater.”

Pattern note: This yarn is doubled throughout the sweater.