Customer loyalty is vital to the success of online stores, which compete in an ever-advancing technological realm. Online shoppers have virtually instant access to the best deals through powerful search engines and competitors are just a click away (Reichheld & Schefter, 2000). E-store loyalty generates repeat sales, increases customers' willingness to pay a premium, strengthens customers' resistance against competitors' marketing effort, and reduces customer acquisition cost as loyal customers are often eager to spread positive word-of-mouth (Roy, Lassar, & Butaney, 2014; Toufaily, Ricard, & Perrien, 2013).

Much research has established that online shoppers' loyalty is significantly and directly affected by the antecedents of perceived website usefulness (PU) and satisfaction (e.g., Cenfetelli, Benbasat, & Al-Natour, 2008; Devaraj, Fan, & Kohli, 2002; Jiang & Benbasat, 2007a; Kim, Ferrin, & Rao, 2009; Koufaris, 2002). It has been shown that evaluations of PU and satisfaction jointly account for more than 54% of the variance in continued usage of e-stores (Cenfetelli et al., 2008). Loyalty develops cumulatively over time as customers make multiple purchases (Keiningham, Aksoy, Malthouse, Bouye, & Lariviere, 2012; Oliver, 1999). It is therefore imperative to go beyond a static understanding of its antecedents to study how their changes affect the development of loyalty. Both offline and online shopping research suggests that PU and satisfaction can change over purchases. As early as the 1980s, LaBarbera and Mazursky (1983) found that customers' evaluation of satisfaction changes significantly from one purchase to the next. A more recent study continued to observe longitudinal change in customers' satisfaction with offline businesses (Keiningham et al., 2012). E-commerce researchers have also argued that evaluations of PU (e.g., Al-Natour & Benbasat, 2009) and satisfaction (e.g., Cenfetelli et al., 2008) change over purchases.