The association of housing affordability with physical and mental health in Hong Kong, where there is a lack of related research despite having the worst housing affordability problem in the world, considering potential mediating effect of deprivation. Methods A stratified random sample of 1978 Hong Kong adults were surveyed. Housing affordability was defined using the residual-income (after housing costs) approach. Health-related quality of life was assessed by the Short-Form Health Survey version 2 (SF-12v2), from which the physical component summary (PCS) and mental component summary (MCS) measures were derived. Multivariable linear regressions were performed to assess associations of housing affordability with PCS and MCS scores, adjusting for sociodemographic, socioeconomic and lifestyle factors. Mediation analyses were also conducted to assess the mediating role of deprivation on the effect of housing affordability on PCS or MCS.

Concerning the methodology to assess housing affordability, the ratio-income approach (ie, housing cost as a proportion of household income with a threshold value specified to indicate unaffordability) is most commonly used. However, this method fails to measure households’ ability to pay for non-shelter necessities, which is likely to differ across income levels given the same proportion of income spent on housing. The residual income (after housing costs) approach may be a better indicator of housing affordability as these measures the absolute amount of income left after housing payments, with a sliding scale in relation to household composition and income levels. Moreover, it reflects more accurately whether a household could meet its non-housing needs within its income constraint. Hong Kong serves as an ideal setting to study the association between housing affordability and health as it suffers from severe housing affordability problems despite being one of the most developed places in the world. In 2018, the affordability ratio of Hong Kong was the highest in the world at 20.9, meaning that the median cost of a dwelling in Hong Kong is 20.9 times the annual median pretax household income, by contrast the ratios were 8.3 in London, 5.5 in New York and 4.6 in Singapore.