“…The primary content of all selected textbooks was pre-algebra, including rational numbers, monomials and polynomials, and first-order equations with one unknown. The content was controlled because previous study suggested that the distribution of definition types and strategies vary on different topics (Ginther & Henderson, 1966). Thus, Sections 1.1 to 4.8 and Sections 12.1 to 12.6 in Bennett et al (2008); Sections 1.1 to 6.2, Section 8.1 and Sections 12.1 to 12.5 in Larson et al (2008); and Chapter 1 to 3 in Kecheng Jiaocai Yanjiusuo ( 2007) were selected for the coding purpose in this study, so that the coded content was the same across different textbooks.…”