Final answer:
Without additional context, it is unclear what the acronym aDDM refers to or which specific aDDM variable stays the same when two items have equal value.
Step-by-step explanation:
When referring to two items having equal value, and considering the context provided by the variables a, d, and g being quantitative discrete, without a specific formula or context such as in equations or probability, it is not entirely clear what the acronym aDDM stands for or to what specific mathematical concept it is referring. However, the context suggests that this might be related to some form of measurement or comparison where variables stay unchanged when items have equal value.
For instance, if 'aDDM' stands for a concept where d is the variable that is supposed to stay constant, and given that a, d, and g are discrete quantities, the unchanged variable could align with option 1) a, 2) b, 3) c, or 4) d based on the provided options. Typically, in probabilities like events A and B, these outcomes represent statistics or discrete variables. Unfortunately, without additional context, the specific aDDM variable that stays the same cannot be determined definitely from the information given.