Above Michael Drake’s desk, at City Hall in Little Rock Arkansas hangs a simple sign:

“In God we trust, everyone else must bring data”

Michael is the Chief Service Officer of Little Rock, responsible for engaging volunteers to help the city meet its most pressing needs. Over his four-year tenure he’s had hundreds of brilliant ideas pitched to him to get volunteers involved in reducing childhood obesity which for decades has stood stubbornly at around 38 per cent across Arkansas.

But he’s learnt that Edwards Deming’s famous quote is a mantra to stick to. Brilliant sounding initiatives didn’t always have a clear theory of change, well branded new approaches didn’t always have any evidence base. Little Rock wanted to do things differently, but quickly built a reputation that it was only interested in well evidenced approaches.

The approach has stood Michael and Little Rock in good sted. It now has thousands of volunteers doing what works: building walking trails, teaching cooking classes, growing food and swapping vending machines for healthy eating trucks and more, all in an effort to reduce childhood obesity.

And it’s proved immensely successful. Arkansas has one of the highest rates of childhood obesity in the USA, but through well-evidenced impact volunteering in seven schools, they have reduced childhood obesity by eight per cent a year amongst the pupils in these schools.

Michael has been over in London with us today, re-telling these stories to inspire the next generation of Chief Service Officers, now in place in Bristol, Kirklees, Plymouth and Portsmouth. As they each embark on finding and implementing the most impactful volunteering opportunities through Cities of Service UK Michael's advice is ringing in their ears - "everyone must bring data".

That means every initiative they implement needs a clear theory of change, its impact must be measured and reported regularly and if the data shows it's not working then it'll be stopped. It's an approach we've long championed through the Alliance for Useful Evidence and other Nesta programmes, but we know it's not always easy to follow through on in practice.

Perhaps we all need a sign like Michael's above our desks for that daily inspiration to ask for the data.