A recent article in the American magazine the Atlantic reported that “Half of all kids are traumatised”, basing the headline on a study of childhood experiences from the US. If you’re shocked by this figure, it’s actually a fairly low estimate as far as the research goes, with many large studies citing figures that show over 70% of people have experienced a traumatic event in childhood.

That rises to 80% or more for adults, and when you reflect on these figures for a moment – suggesting that four out of five adults have been traumatised – it raises the little-asked but important question – what is trauma?

Although definitions vary, the implications are not purely academic, as service funding, legal compensation and treatment decisions rest on what we recognise as traumatic. The term originally referred to a bodily injury, and it is still used this way in medicine. During the birth of psychology, its meaning was extended to include the concept of a psychological injury – the idea that some events can be so emotionally powerful that they leave a “scar” in the psyche. Early 20th-century theories suggested that a traumatic event was only significant for its ability to reveal an innate character weakness. Although far fewer British soldiers were shot for “cowardice” than is assumed, it is true that they were occasionally executed for what we would now see as trauma.

These theories took a surprisingly long time to overturn, and it wasn’t until well after the second world war that our thinking, thankfully, changed, and our modern concept of trauma took hold. We now understand that everyone has their limit in terms of stress, but the boundaries of what we accept as trauma are still disputed. Much of the current debate surrounds how much emphasis should be placed on what happens to you, compared to the consequences of the experience.

Some of the confusion arises when we talk about “being traumatised”. Let’s take a typically horrifying experience – being caught in a war zone as a civilian. This is often described as a traumatic experience, but we know that most people who experience the horrors of war won’t develop post-traumatic stress disorder or PTSD – the diagnosis designed to capture the modern meaning of trauma. Despite the fact that these sorts of awful experiences increase the chances of acquiring a range of mental health problems – depression is actually a more common outcome than PTSD – it is still the case that most people won’t develop them. Have you experienced trauma if you have no recognisable “scar in the psyche”? This is where the concept starts to become fuzzy.

One attempt to define events, apart from reactions, as traumatic is written into the PTSD diagnosis itself, but this definition has changed every time the diagnostic manual has been revised. A particularly contentious issue has been whether you have to be directly involved in the event for it to count. Previously, this wasn’t the case, so you could still be recognised as traumatised if, let’s say, a relative was kidnapped. But the flexibility of the definition led to waves of people reporting post-traumatic stress after seeing news reports of events in which they had no personal involvement, and also led to some findings that were hard to square with the original idea of trauma. One such study, on the Boston marathon bombings, found that people who saw the news reports were more likely to report trauma symptoms than the people who were actually caught up in the terrorist attack.

In an attempt to avoid these problems, the definition of trauma, at least for PTSD, changed again. The result was a compromise where exposure to the event through “electronic media” now doesn’t count, unless it’s part of your job – such as reviewing evidence in police work. The fact that we have these increasingly convoluted definitions shows that we are still trying to negotiate the borders of what is considered to be traumatic.

Alongside the attempt to define it medically, there are lots of other concepts of trauma as something that damages our trust in others, shatters our self-image or has scarred the social or cultural history of a people. Over time, trauma has also acquired a sort of social weight, a value that suggests some sort of reparation is required. Anthropologists Didier Fassin and Richard Rechtman have called this the “moral economy of trauma”. It’s a remarkable transformation of meaning in light of the fact that trauma was considered a sign of bad faith for most of the last century, but it has meant that a lot of problems get reframed as trauma as a way of trying to lend them rhetorical importance.

The study that gave rise to that “half of all kids traumatised” headline actually looked at lots of difficulties, including poverty, divorce and prejudice, with any violent results of these situations being categorised separately. All clearly negative… but not necessarily traumatic in the way it is usually defined.

The recognition of trauma, in the clinical sense, has been an important advance in mental health but its use in public debate sometimes obscures the fact that there are many forms of social damage and many sources of mental health problems that don’t need to be traumatic to be worthy of attention. The next advance will be recognising other problems as equally important.