Like all students of wrongness, I'm fascinated by research into irrational beliefs and behaviours, but I'm also suspicious of how far you can stretch the findings from a laboratory into the real world. A cracking paper from Social Psychology and Personality Science makes a neat attempt to address this shortcoming.

Loran Nordgren and Mary McDonnell wanted to see whether we perceive a crime as being more serious when more people are affected. Sixty students were given an article about a fraud case; in one version three people were defrauded by a financial adviser, in a second, 30. All other information in the story was the same in both versions.

You might imagine that someone who harmed more people would be deemed to deserve harsher treatment. But asked to evaluate the severity of the crime and recommend a punishment, participants who read the story with three victims rated the crime as more serious than those who read the same story with 30 victims.

More than that, they acted on this view: out of a maximum sentence of 10 years, people who read the three-victim story recommended an average prison term one year longer than the 30-victim readers. Another study, in which a food processing company knowingly poisoned customers to avoid bankruptcy, gave similar results.

It's nice that they did two studies of the same idea, but I always worry about experiments like this, because they demonstrate an effect in the rarefied environment of the laboratory, while the real world can be much more complicated.

But this paper has two halves: the authors then go on to examine the sentences in a representative sample of 136 real world court cases, in which people were found guilty of these kinds of crimes but with varying numbers of victims, to see what impact the victim-count had.

The results were depressing. These were cases between 2000-2009 in which individuals from corporations had been found guilty by juries of negligently exposing members of the public to substances such as asbestos, lead paint or toxic mould, and their victims had all suffered significantly. The researchers' hypothesis was correct: people who harm larger numbers of people get significantly lower punitive damages than people who harm a smaller number. Courts punish people less harshly when they harm more people.

It seems to me that alternative explanations may play a contributory role: cases where lots of people were harmed may involve larger companies, with more expensive and competent lawyers, for example, or larger and more deniable lines of responsibility. But in the light of their earlier experiment, it's hard to discount the contributory effect of empathy, and this is a phenomenon we all recognise.

When he appeared on Desert Island Discs, Rolf Harris told the story of his song "Two Little Boys". His uncle died in the war, but Rolf's dad always believed that if they'd only been in the same infantry unit, he could have crawled out and pulled his little brother to safety, just like in the song. Instead he lay, bleeding to death from his injuries, and died above the trench. Rolf played Two Little Boys to his grandmother once. She sat through it quietly, took it off at the end, and said: "Please don't ever play that to me again."

I'm sure it's lame of me, I realise it may not press your own personal buttons, but this story made me cry a tiny bit. Two million people die of Aids every year. It never has the same effect.