Another way of studying the eﬀects of income on happiness is to study the relation between average incomes and average happiness for whole countries. There have been a number of studies like this, using up to 55 countries. All have found a strong correlation of about .60 (Diener and Biswas-Diener, 2000). Comparing the richest and poorest nations there is a diﬀerence of about 7 out of 30 units of the Satisfaction With Life Scale, a quarter of the whole scale. Some studies found a levelling oﬀ part of the way up the income scale, but other studies did not. Diener et al. (1995) did not ﬁnd any levelling oﬀ, and they found that per capita GDP and average purchasing power correlated with satisfaction at .33 and .37 with basic need fulﬁlment held constant.