"The Duplication of Purchase Law stipulates the relationship between the duplicated purchases of two competitive or complementary brands and their market shares."

"Results indicate that the law applies well across time and nations; the duplications of games played are highly correlated to games’ penetration rates."

"Together, they generated about US$89 billion in gross gambling revenue in 2009 (The United States Census Bureau, 2012)."

"While the total gambling revenue in Australia in 2008–09 exceeded US$15 billion (Productivity Commission, 2010), Macao's gross casino revenue reached a whopping US$33.5 billion in 2011 (Gaming Inspection and Coordination Bureau, 2012)."

"One exception is Lam (2006), who found that gambling purchases in the United States followed a regular pattern of cross-buying."

"When one considers consumers in aggregate, many markets follow simple empirical ‘marketing laws’ (Ehrenberg, 1959)."

"According to Uncles et al. (1995), the key factor for the purchase duplication between any two brands is the penetration of each brand. This regularity is commonly called the Duplication of Purchase Law"

"In line with the consumption of many consumer products, the results of this study showed that gambling purchases in all three jurisdictions under consideration obeyed the Duplication of Purchase Law;"