"How many times has the Doctor been seen singing in the series?"
From Tardis Wiki, the free Doctor Who reference
"How many times has the Doctor been seen singing in the series?" was an "important stud[y]" conducted by DWM sometime prior to September 1992. It paved the way for the magazine to answer the question "How many times has the Doctor been seen blinking since 1963?". (NOTVALID: The Year Ahead)