We’ve always been pretty sceptical about the “results” agencies stick at the bottom of case studies or enter into awards. You know the sort of thing: doing x (whether that’s a new tone of voice, rebrand or whatever) has increased sales by 900% and brand awareness by five dog years. Because, as any good statistician will tell you, ‘correlation’ (that something happened) is different to ‘causation’ (especially if, say, ice cream sales went up during a heatwave).

But for once, we have some impressive stats that don’t have anything to do with anyone else – or the weather.

We’ve been working for a company called Utility Warehouse. If you don’t know them, they supply energy, broadband and phones on a single bill for a good price. We’ve been helping their teams write to customers who have questions and complaints. When we started the training back in July we had some resistance, which often happens, especially from people who’ve been somewhere a long time and are used to writing in a set way. But, little by little, we got them on side. The more people we trained, the more our training percolated around the teams. Until, by the end, it was less ‘why should I write differently?’ and more ‘can you help me write differently?’

Now for the stats. Their Net Promoter Score (NPS for short, which measures how likely someone is to recommend a business to a friend or colleague) went up 100% following our training. Chris, the head of their customer service team, sat me down in front of some spreadsheets and explained what was going on. You could actually see the score shoot up from September and then slowly carry on rising to January.

A common concern that comes up in training, especially from people who have targets to meet, is that “writing like this will take much longer”. And the stats backed that up – at first. In September, their teams were writing fewer emails and letters (but at least customers were happier). But then, as they got more confident, the pace went up – too quick at one point as they got too confident – and then levelled out again from December to January. But up they stayed. Chris said that following the training, a team of 30 were writing 240 more emails a day. In pounds and pence that’s equal to the salary of one person. Never mind the NPS scores, the training has paid for itself in output alone.

As I was about to leave, Chris beckoned me back to show me one more thing. A newsletter email had been sent out to customers a week or so ago. And within minutes, a couple of his team emailed him – off their own backs – with suggestions about how to improve it. “That would never have happened before the training”, Chris said. Which shows something that’s almost impossible to measure – good writing changes the way people think about their work too.