“…This said, certainty about the existence of trends is often impossible (Heckman, 1991;Stock & Watson, 1999). Although de-trending data is often recommended (e.g., Curran & Bauer, 2011;Curran, Lee, Howard, Lane, & MacCallum, 2012;Hoffman & Stawski, 2009), there is no single way to do this, and tests for trends are often ambiguous (Davidson, 2013;Haldrup, Kruse, Teräsvirta, & Verneskov, 2013). The fact is that the evolution of any system involves mixtures of multiple processes, leading some to say that "no one really understands trends, even though most of us see trends [in] data" (Phillips, 2003, p. C35;Heckman, 1991).…”