Final answer:
The primary difference between existing (prescriptive) and planned (descriptive) models is that prescriptive models guide expected outcomes based on established procedures, while descriptive models are designed to visualize and predict future outcomes, aiding in planning and modifications.
Step-by-step explanation:
The difference between existing (prescriptive) and planned (descriptive) models refers to the way these models are used to understand and predict outcomes in various contexts, such as population changes or product development. Prescriptive models are those that have been established over time and are currently used as a guide for expected results, while descriptive models are carefully designed plans intended to predict and shape future outcomes.
For example, when an architect creates a scaled physical representation of a planned office building, it's a descriptive model that shows how a city block will look after construction.
This model helps stakeholders visualize the outcome before it's built. Similarly, companies often create models of new products; these are descriptive and allow demonstration of how the product will work, even if it's not the final version. Prescriptive models, on the other hand, are based on long-standing practices that are often in the process of being modified to increase predictive ability, as our understanding of the systems they describe evolves.