1. Not to any great degree, there is: The epidemiology of chronic fatigue in San Francisco from which: "CFS- and ICF-like illnesses were most prevalent among women and persons with annual household incomes below $40,000, and least prevalent among Asians. The prevalence of CFS-like illness was elevated among African Americans, Native Americans, and persons engaged in clerical occupations. Although CFS-like cases were more severely ill than those with ICF-like illness, a similar symptom pattern was observed in both groups. In conclusion, conditions associated with unexplained CF occur in all sociodemographic groups but appear to be most prevalent among women, persons with lower income, and some racial minorities." ScihubDo we actually know how ME is distributed across social classes? Then, do we know how charitable giving is distributed across social classes?
If there is a big mismatch, then that may be a part of the problem.
I would surmise but I can't quote evidence that certain cultural backgrounds have a history of charitable giving and others don't. This may or may not be related to income. This doesn't seem very helpful but it's trying to tease out why private giving is lower in ME, if it is, than many other illnesses.
I agree that invisibility of the condition seems likely to be a factor.
2. There is data. However caution is needed when extrapolating across countries/cultures. There's quite a lot of social psychology work e.g A Large Scale Test of the Effect of Social Class on Prosocial Behavior but all the usual caveats on 'psych' research apply. The Charities Aid Foundation carries out an annual review of giving but doesn't use socio economic status but these reports are important to understand the broader picture. The UK Department of Culture, Media and Sport produced a report - data via Statistia which showed a distinct socio-economic disaparity for those areas under the DCMS purview - excludes health !
My argument was not so much about levels of giving - but literally levels of engagement, so that understanding of the problem is not a measure of how much cash is donated but about who is and who is not is becoming a member of a group or seeking support from a patient organisation and what kind of sustained relationship different people are having with patient led structures.