70 During the past 30 years, much more information has become available on …. A considerable amount of literature has been published on X. These studies …. The first serious discussions and analyses of X emerged during the 1970s with …. What we know about X is largely based upon empirical studies that investigate how …. General reference to previous research or scholarship: normally more than one author Traditionally, it has been argued that …. (Smith, 1982; O’Brien, 1984). Surveys such as that conducted by Smith (1988) have shown that …. Many historians have argued that …. (e.g. Jones, 1987; Johnson, 1990; Smith, 1994). There is a consensus among social scientists that ….(e.g. Jones, 1987; Johnson, 1990; …. Recent evidence suggests that …. (Smith, 1996; Jones 1999; Johnson, 2001) Recently, in vitro studies have shown that X can …. (Patel et al., 1997; Jones et al., 1998). Several studies investigating X have been carried out on ….
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