The biological/scientific definitions of heredity and heritable differ slightly from the popular usage. Lay people tend use it to mean “how much is this caused by genes?” In science, heredity is how closely people resemble their parents, divided by the total variation in the population. Biological sex has almost zero heritability because knowing someone’s parents sex does not allow you to predict their own sex.* Number of arms is barely heritable, because there’s almost no variation in number of arms among humans, and what variation exists is overwhelmingly caused by environment, not genetics.
A corollary to this is that a measure of heredity is only valid for the exact environment you measured it in. If you plant a variety of seeds in identical pots and give them identical water and supplements, most variation will be due to genetics, and a small amount to chance (which will be counted as environment), so traits like height and time to flower will be highly heritable. If you plant those same seeds in widely varying pots and vary the water and nutrients they get, a lot of the variation will be due to environment, and the heredity values of the same traits will be much lower. Skin color in Norway is more heritable in the winter than in the summer, because teenagers deliberately tan more than their parents.
I have struggled before to make effectiveness estimates when the intervention’s usefulness depends on multiple factors. Blood for car accident victims is only helpful in the context of emergency rooms and medical schools and sterile gauze. Suicide hotlines require phones and electricity and suicidal people at a bare minimum, and active rescues require police and mental hospitals and often pharmaceutical research. I think I’m just going to have to put effectiveness in the same category as heredity: the quantification is only valid for the environment in which it is measured.
I’ve worried before about Effective Altruism’s tendency to take the existing system as a given. That was a reasonable simplification when the movement was first starting, and there was plenty of low hanging fruit that didn’t require more sophisticated analysis. But I’m really happy to see organizations like the Open Philanthropy Project branch into studying how to change systems and how to measure the effectiveness of attempts to do so.
*Intersexuality confounds this a little but my impression is it’s mostly not a genetic issue, in part because intersex people generally have difficulty reproducing.