One possible explanation for this is that as nations become richer, people place higher value on health and want to spend a larger share of their income on improving their health (Fogel 2008). The “income elasticity” varies a lot in empirical results and whether health care is a luxury' good or a necessity is still an unsettled issue. Results for the US and Canadian provinces, as well as national-level data for 16 OECD countries, confirm that estimates of the size of the income elasticity vary by level of analysis, with international income elasticity generally larger than elasticities estimated in national or regional studies (Di Matteo, 2003).