"The 17,000 or so patients in this study were mostly middle-aged white people, upper- and middle-class, from San Diego."
It's true that there are a lot of variables when asking broad questions like what causes poor health, but it seems like the majority of the participants weren't of a lower-socioeconomic demographic, as indicated in the article.
It is "adjusted for age, gender, race, and educational attainment."
84% where white.
59% of Americans identify as middle class, upper-middle or upperclass. So saying that the study used mostly upper- and middle-class doesn't really tell us anything.
Ironically, the only link to the word "income" on that page was a related story-link, "People With Low Incomes Say They Pay A Price In Poor Health".
I remain unconvinced that "Family Secrets Make You Sick" based on that article. There are a lot of ways to determine whether that might be the case, but I'm surprised, based on the article's description, that they were able to get a paper published with their method.
It's true that there are a lot of variables when asking broad questions like what causes poor health, but it seems like the majority of the participants weren't of a lower-socioeconomic demographic, as indicated in the article.