In 2013 the UK government tested eight versions of one web page on more than a million people.
The page appeared right after drivers renewed their car tax online and asked them to join the organ donor register. One version said nothing. The rest each added one line. One warned that three people die every day because there aren't enough organs. Another promised you could save or transform up to nine lives.
A version with a photo did worse than the page that said nothing: 2.1% signed up, against 2.3% for the blank one. I'd have bet on the photo, and I write for a living.
The winner was a plain question. "If you needed an organ transplant would you have one? If so please help others."
3.1% signed up. The fear line got 3.0%, so call those two a tie. Rolled out across 25 government websites, the page with that question collected 529,000 registrations by October 2017.
Nobody knew which line would win until a million people answered with their clicks.
Your homepage headline is somebody's best guess too. When did it last go up against a second version?
Tell me in the comments which line you'd have bet on.