Association Between Adult-Onset Hearing Loss and Income: A Systematic Review.

All 46 studies took a single snapshot in time, so they show that lower income and hearing loss go together but cannot say which came first. The authors state they cannot infer cause. Hearing loss was defined differently across the studies: 24 measured it with hearing tests and 22 relied on people saying they had hearing loss, and the definition used changed from study to study. Self-report can be swayed by memory, by wanting to give the 'right' answer, and by how people read the question. Income was also defined differently. Some studies split people into low, middle and high income, some used a broader measure of social position that included income, and some used the ratio of income to the poverty line. All of it was self-reported, which carries a risk of inaccurate recall. Only nine of the 46 studies reported participants' ethnicity, and in those nine, people from racial or ethnic minority groups were under-represented. Eight of the nine were based in the United States. No studies came from low-income countries, and the authors suggest this may be because their search was limited to income rather than broader measures of wealth such as assets. The studies were too varied in design, definitions and analysis for the researchers to combine their results, so there is no single pooled estimate of the size of the link. Nine studies looked at sex or gender differences, but the studies used the words 'sex' and 'gender' interchangeably, so it is often unclear which one they actually measured and the mixed findings are hard to interpret. One included study had 441 participants; the rest analysed more than 1,000 people each.

The article text supplied does not include a funding statement or a competing-interests declaration, so there is nothing to report on who paid for the work.

Do not read this as hearing loss causing lower income, or as a reason to expect that treating hearing loss will change anyone's earnings. All 46 studies were single snapshots in time, so the direction of the link is unknown, and the authors say so themselves.