J. P. Guilford (1967) has indicated that creativity and creative problem solving (CPS) are the most complex mechanisms in human mind. The similarity between these two abilities lies in the fact that “both must transform pre-knowledge and experience to further produce new products or responses.” Torrance (1991) stressed that CPS is one of the most effective ways to foster students’ creativity in different aspects of life. CPS is a higher-order thinking which integrates creative thinking and problem solving. Many previous studies on problem solving (e.g. Jhan & Wu, 1991; Chang & Wong, 2002; Cropley, 1999; Mumford, et al., 2002) stressed the importance of integrating creativity into the process of problem solving, instead of just solving problems through static and mechanical ways. It is well accepted that CPS is a creative thinking skill which can be widely applied in different fields and help to solve life problems as well as learning problems in the classroom (Cheng, Liu, & Chang,2007; Tang & Chiu, 1999).In decade, many scholars have intended to explore the components of problem solving and to analyze thinking models and strategies used by problem solvers (e.g., Mayer, 1998; Treffinger, Isaken, & Dorval, 2000; Mumford, Decker, Connelly, Osburn & Scott, 2002; Isaksen,  & Parnes, 1985; Isaksen, Dorval, & Treffinger, 2011). The most influential CPS model was proposed by Parnes (1977), which consisted of (1) fact-finding (FF): collecting data and information using 5 self-strategies (who, what, where, when, why, how); (2) problem-finding (PF): clarifying problems to make them more explicit; (3) idea-finding (IF): finding variable ways to solve problems; (4) solution-finding (SF): seeking criteria for evaluating ideas to reach a more feasible solution; (5) acceptance finding (AF): evaluating solutions and confirm efficiency or not. The five componential steps progress in a cycling process.

      Based on the Creative Problem Solving model proposed by Parnes (1977), the study aimed to develop the Creative Problem Solving Test (CPST) for primary school students of medium and high grades. CPST was designed in the form of testlet to measure pupils’ creativity in real-life problem solving, including the abilities to observe, define, analyze and solve problems. In traditional, standard item response models (e.g. multidimensional analysis) were conducted to analysis data and overlook the high correlations between items. However, standard item response models to testlet responses tend to overestimate the precision of measures obtained from testlets and yields biased estimation for item difficulty and discrimination parameters (Wang & Wilson, 2008). To obtain more precise and adequate estimates, this study conducted the Rasch testlet model (Wang & Wilson, 2008) to assess model-data fit of the CPST and testlet effect.

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