Final answer:
A differentiation strategy is least effective in commodity goods markets where products are uniform and competition is based on price rather than features.
Step-by-step explanation:
The use of a differentiation strategy would be expected to be least effective in the market for commodity goods. In markets with a high degree of variety, like motion pictures, popular music, and writing instruments, firms have more scope to differentiate their products based on style, features, and branding. However, commodity goods are typically uniform and undifferentiated, such as agricultural products or raw materials, where competition tends to be based on price rather than on differentiated features.