“…In this study, we conducted a literature review and summarized the factors that affect national patent quality through the use of a patent analysis. Previous studies have reported that the factors affecting patent quality include patent family size (Harhoff et al, 2003;Harhoff and Reitzig, 2002;Lanjouw and Schankerman, 2004), number of claims (Lanjouw and Schankerman, 2004;Sapsalis et al, 2006;Munoz and Grana, 2016), number of international patent classifications (IPCs) (Harhoff et al, 2003;Lerner, 1994), forward citations (Fisch et al, 2016;Hall et al, 2005;Popp et al, 2013;Sterzi, 2013), backward citations (Harhoff et al, 2003;Lanjouw and Schankerman, 2004), nonpatent references (NPRs) (Branstetter, 2005;Callaert et al, 2006) and maintenance time (Bessen, 2008;Schankerman and Pakes, 1986).…”