“It’s time to talk” is a campaign currently being promoted by Time to Change, a charity whose aim is to change attitudes to people with mental ill health. On the charity’s website a banner tells us: “1 in 4 of us will experience a mental health problem at some point in our lives, but we still don’t talk about it. What are we afraid of?”

This “one in four” figure has also appeared in government speeches1 and NHS publications.2 It is the name of a short film and the title of a mental health magazine.

Yet it is not always clear to what the figure refers. Time to Change seems to be referring to lifetime prevalence, while a 2010 advertising campaign by Islington Primary Care Trust stated, “One in four people will experience mental health problems each year.” A statement on the Royal College of Psychiatrists’ website reads, “One …