Everything else is ready: study the parts, the key terms and the quiz below.
How Charts Can Mislead
Detect when visual choices change the apparent size or shape of an effect without changing the underlying observations.
In this lesson6 parts
- 01A true change inside a misleading claim
- 02The axis changes appearance, not observations
- 03The date range changes the claim
- 04Aggregation and smoothing can hide local changes
- 05Units and encodings must remain auditable
- 06Code, corrected report and challenge
Key terms
The words this lesson introduces, each in one line. The module’s glossary collects them all.
- unit
- The quantity a chart's axis measures: pounds of gross positive invoice value, or a count of invoices.
- relative change
- Difference divided by the starting value: 22.57% between the weeks starting 2011-10-31 and 2011-11-07.
- axis baseline
- The value at the start of a chart axis.
- truncated axis
- An axis whose displayed range omits lower values.
- bar encoding
- Magnitude represented by length from the baseline, which is why a bar axis starts at zero.
- displayed time window
- The dates included on a chart.
- incomplete interval
- A displayed time bin extending beyond the source's recorded period, such as the week containing 2011-12-09.
- aggregation window
- The span of source dates combined into one reported value.
- rate per week
- An amount divided by the number of complete weeks it represents.
- smoothing
- Replacing nearby values with a declared local summary, such as a three-week moving average.
- moving average (narration)
- The mean of each value and its neighbors; a centered three-week one uses the week and the weeks either side.
- frequency density
- Bin count divided by bin width, used when histogram bins have unequal widths.
- dual axes
- Separate vertical scales placed on one plot; either can be rescaled until two lines look aligned.
Quiz 5 questions
Your first pick on each question is the one that counts, and a right one earns a coin. Getting one wrong here is how the lesson sticks.
Practice
Problems to solve in your own notebook. Each states the problem, not the steps: working out the steps is the exercise. Level A applies the lesson, B combines it with earlier ones, C stretches it.
The self-checking notebook for this lesson is Stats 2.1, 2.2 and 2.7 · EDA and a chart audit.
Common mistakes
What you will see when it goes wrong, why it happens, and the fix.
Where it’s used
Where this lesson’s ideas turn up in real work.