Measuring Knowledge of Acids and Bases as Continuous and Categorical Constructs toward Understanding Concept Progression

We describe the development and validation of the Measure for Conceptualization of Acids and Bases (MCAB) for college students. Items were constructed based on a learning progression framework of acids and bases (Lin and Chiu, 2007). After thorough content review, continuous and categorical scales were constructed using Rasch and Latent Class Mixture Model frameworks, respectively. A valid and reliable 28-item instrument was the outcome of two rounds of data collection and revision. The Rasch scale was shown to be reliable and unidimensional, and the items fit well with the Rasch model. Latent Class Analysis (LCA) showed that the data were described adequately by a 2-class scale. Students in Latent Class 1 demonstrated conceptions of acids and bases consistent with the phenomenon and character-symbol models (Lin & Chiu, 2007). With some exceptions, the students in Latent Class 2 demonstrated conceptions consistent with the scientific model (Lin & Chiu, 2007). Rasch score predicted Latent Class with 93% accuracy, demonstrating that classes derived from LCA are a “progression” in the sense that we use the word. Use of Rasch and LCA models toward generalized understanding of how college students conceptualize acids and bases is discussed.