Structural models for combining items (top) and contrasting conditions (bottom) with four indicators (a,b,c,d) for each condition (1, 2), where the effect is represented as a difference score (Condition1 – Condition2). The combining items model assumes that (a) the subtraction reverse codes Condition2 scores to match scale interpretation with Condition1 (e.g., higher values=more of construct), (b) conditions can be decomposed, and (c) both conditions are indicators of a single construct. The contrasted conditions model assumes that (a) scale interpretation is matched before subtraction occurs, (b) the conditions cannot be decomposed meaningfully, and (c) the construct is revealed by the comparison of interdependent conditions.