That’s right. Studies will say that they “control for age and income” but even doing just that is probably not possible, unless a) you break a number of laws a

That’s right. Studies will say that they “control for age and income” but even doing just that is probably not possible, unless a) you break a number of laws and ethical rules and b) you have a population of hundreds of billions of humans to study. Humans are very different from one another in important but subtle ways.