QUOTE There are two ways of citing, active and passive. In active citation, the cited work or its authors become an ordinary part of the sentence, as a noun, either as a subject, an object, an indirect object or a prepositional object. Two examples: Eriksen et al (2011) studies experimentally the effect of tournaments on effort and risk taking. In Kobila (1991) we find the following proof... By contrast, a passive citation would look like this: There were many other papers published in the same issue of the Scandinavian Journal of Economics (e.g. Fiva and Kirkebøen (2011) or Pesola (2011)) UNQUOTE
Though not sure, but it appears that active citations are those which may prove sufficient to grasp the concept when quoted in a study, while as a passive citation may refer one to a source for further reading. Simply a concept of referencing and cross referencing.
QUOTE There are two ways of citing, active and passive. In active citation, the cited work or its authors become an ordinary part of the sentence, as a noun, either as a subject, an object, an indirect object or a prepositional object. Two examples: Eriksen et al (2011) studies experimentally the effect of tournaments on effort and risk taking. In Kobila (1991) we find the following proof... By contrast, a passive citation would look like this: There were many other papers published in the same issue of the Scandinavian Journal of Economics (e.g. Fiva and Kirkebøen (2011) or Pesola (2011)) UNQUOTE