In 2007, British psychologist Oliver James asserted that there was a correlation between the increasing occurrence of affluenza and the resulting increase in material inequality: the more unequal a society, the greater the unhappiness of its citizens. Referring to Vance Packard's thesis "The Hidden Persuaders" on the manipulative methods used by the advertising industry, James related the stimulation of artificial needs to the rise in affluenza. To highlight the spread of affluenza in societies with varied levels of inequality, James interviewed people in several cities including Sydney, Singapore, Auckland, Moscow, Shanghai, Copenhagen and New York.