An older person's handshake can say more about their education than a diploma on the wall. In three parts of the world, the US, China, and Europe, researchers had tens of thousands of people over fifty squeeze a dynamometer, and they saw that education works like a lever that lifts muscle strength, but the length of that lever depends on where a person was born.
Europeans turned out to be the strongest: on average, their grip squeezes 34.3 kg, about as much as a big sack of potatoes. Americans were the weakest: 28.8 kg, roughly the weight of an average carry-on suitcase. Chinese people landed in the middle at 31.0 kg. Strength fades with age for everyone, but the gap between Europe and the US grows: at 50 it is just 1 kg, and by 80 it is already 4.5 kg, the difference between a bag of sugar and a bag of flour.
But the most interesting part is hidden in how education distributes strength within each country. In China, the gap between the most educated and the least educated turned out to be the largest: an inequality index of 4.22 versus 2.77 in Europe and 1.67 in the US. At the same time, the payoff from education for an individual Chinese person is the smallest: men gain just 1.84 kg, and women 0.79 kg, less than a stick of butter. So here is the paradox: the lever is short, yet the gulf between those who managed to grab it and those who did not is the deepest of all.
Body mass index, often blamed for weakness, played an unexpected role. It turned out not to explain the link between education and strength but to hide it. More educated people are leaner, and lower weight is linked to lower grip strength. If you do not account for this effect, the advantage of education looks weaker than it really is. In the US, this masking contribution was minus 7.4%, in Europe minus 4.8%. In other words, extra weight in less educated people partly compensates them for a lack of muscle strength, and the true gap turns out to be wider.
The handshake that opened this story sounds different in different countries. In Europe it is firm and confident, and education there is a long lever that helps everyone lift their strength. In China the lever is shorter, but the gulf between those who have it and those who do not is wider, especially for women. Which means that simply giving someone an education is not enough: the lever has to work the same way for everyone, regardless of gender or a country's history.
The difference in grip strength between European and American men with high education reaches 3.48 kg, comparable to the weight of a small cat.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.