Can a kind word change your life? I know from experience that it can. More than three decades ago, during the summer vacation at the end of my first year at university, I received a handwritten letter from my economics tutor, the effervescent and much-missed Peter Sinclair.

I’d been planning all along to drop economics in favour of other subjects, but Peter congratulated me on my end-of-year exam results, emphasised that those results were stronger than I might realise, and encouraged me to keep going. I decided to stick with economics after all.

I hope I can be forgiven my double take when I stumbled upon a recent working paper published by two academic economists, Olivia Edwards and Jonathan Meer. Their research answers a simple question: what happens if you do exactly what Peter Sinclair did for me, but on a much larger scale?