Principal components analysis (PCA) was used with each scale to obtain evidence of construct validity. The first
two scales were taken from the original SAIS: Attitudes Toward Science (ATT) and Student-Centered Teaching
Practices (SC). The third scale, Teacher Demonstrations (DEMOS), consisted of the two additional items of the
SAISv.3. Because multi-factor models are less constrained than single factor models, two measured variables per
factor are allowed as long as they are permitted to correlate. With single factor models at least four measured
variables are required (Kaplan, 2000).