Question: In a concise analytical response, explain the limitation of relying only on the dev-error curve and the role of the training-error plot.

Sample answer: Relying only on the dev-error curve can make it difficult to extrapolate and predict exactly where the curve will go if more data is added. Plotting training error supplies an additional view that can help estimate the impact of increasing the amount of data. It should therefore be treated as a supplement to the dev-error curve when considering more data.

Key points:

• The dev-error curve alone can be difficult to extrapolate.
• The prediction concerns where dev error may go with more data.
• Training error supplies an additional plot.
• The additional plot helps estimate the impact of adding data.

Rubric: A strong response identifies the extrapolation difficulty, connects it specifically to predicting the dev-error curve under more data, and explains that training error is an additional plot that helps estimate the impact of adding data.