Change over time
Indexed / rebased line chart
Rescales series to a common reference value to compare relative changes.
- Chart
- Trend over time
- Comparison
What it answers
Which series grew faster relative to its starting point?
- Shape
- Lines with a shared starting index
- What it shows
- Relative performance and growth divergence.
Example
The question
Which cost line has grown fastest since January?
Cost lines indexed to January 2025 = 100
Illustrative data. It belongs to no company.
When to use it
Use it when
Comparing relative growth across differently sized series.
Avoid it when
A zero base value or a question about absolute levels.
How to read it
Read every series from the shared index base and compare later index values.
Note
Specify base period and index. Zero base values need another method.
The data you need
- Layout
- Long table
- Fields
- Time: date/datetime; Series: text; Value: number
- One row is
- One series observation at one time. What is the grain?
- Rules
- Sort time within series. Resolve duplicate time-series pairs and align series before stacking.
- Optional
- Wide alternative: Time,A,B with one row per time.
- Preparation
- Choose a common base period and set each series to Value/BaseValue times the chosen index, such as 100. Handle zero base values separately.
- Units
- Index points relative to a chosen base, commonly 100. Relative change from base is Index/BaseIndex-1.
Worked example
Data A100 to 120; B50 to 65. Rebase both to 100. End indices 120 and 130 show B grew faster.
| Time | Series | Value |
|---|---|---|
| 2026-01-01 | A | 30 |
| 2026-01-01 | B | 45 |
| 2026-02-01 | A | 34 |
| 2026-02-01 | B | 40 |