Multiple Line Graphs — Revision Notes

⚡ 30-Second Revision

Read actual time intervals.
Level, change and growth rate differ.
Rate = change ÷ elapsed time.
Equal indices do not mean equal original quantities.
Connecting lines do not prove intermediate observations.

2-Minute Revision

Compare line series using the metric named in the question. A large value may grow slowly, and a larger total change may occur over a longer interval. Use the earlier value for percentage growth and elapsed time for an average rate. Distinguish observed points from interpolation, and preserve the base-period meaning of indices. Co-movement alone does not establish causation.

5-Minute Revision

Series P rises from 40 in 2021 to 70 in 2024; series Q rises from 50 in 2023 to 66 in 2024. P's total increase is 30, but its average annual increase is 10. Q increases by 16 in one year, so its average annual increase over the stated interval is larger. P's endpoint is nevertheless higher. Explain why these comparisons answer different questions and why the data do not reveal P's value in 2022 without an additional assumption.

Vyyuha Quick Recall

Value, Change, Time, Base: identify which of these the question compares.