[nradov]

I generally agree, however socioeconomic and environmental factors are highly correlated with certain medical conditions (social determinants of health). In some cases even causative. For example, patients who live near an oil refinery are more likely to have certain cancers or lung diseases.

https://doi.org/10.1093/jncics/pkaa088

[dekhn]

Studies like that, no matter how careful, cannot say anything about causation.

[onlyrealcuzzo]

So that's the important part, not that they're low income.

[thereisnospork]

Sure, but correlation is correlation. Ergo 'low income', as well as affections or causes of being 'low income' are valid diagnostic indicators.