Verify calculations with executable evidence
Distinguish percentage-point change from relative change.
Reviewed: 2026-10-03
Source-based teaching example · Fictional data
Narration: Microsoft Mark · locally synthesized

00:00:00.000 — What you will learn

Distinguish percentage-point change from relative change.

Visual description:
Distinguish percentage-point change from relative change.

00:00:06.417 — The idea

Compare rates when groups have different totals. Name the measure you report. A numerical difference does not by itself prove what caused the change.

Visual description:
Compare rates when groups have different totals. Name the measure you report. A numerical difference does not by itself prove what caused the change.

00:00:18.750 — One useful term

Percentage point. The direct difference between two percentages.

Visual description:
The direct difference between two percentages.

00:00:26.292 — A worked example

Four errors in twenty tasks is twenty percent. Three errors in thirty is ten percent. The drop is ten percentage points, or a fifty percent relative reduction in the rate.

Visual description:
Four errors in twenty tasks is twenty percent. Three errors in thirty is ten percent. The drop is ten percentage points, or a fifty percent relative reduction in the rate.

00:00:41.000 — Your turn to think

Does “ten percentage points” mean the same thing as “ten percent relative reduction”? Pause and decide before continuing.

Visual description:
Does “ten percentage points” mean the same thing as “ten percent relative reduction”?
Pause the video if you need more time.

00:01:00.083 — Why this answer works

No. The first subtracts rates; the second divides the change by the starting rate. These constructed counts do not prove causation.

Visual description:
No. The first subtracts rates; the second divides the change by the starting rate. These constructed counts do not prove causation.

00:01:12.292 — Check 1

Check counts and the totals you divide by.

Visual description:
Check counts and the totals you divide by.

00:01:17.667 — Check 2

Label the type of change.

Visual description:
Label the type of change.

00:01:22.292 — Check 3

Do not assume tasks were equally difficult or that AI caused the change.

Visual description:
Do not assume tasks were equally difficult or that AI caused the change.

00:01:29.625 — Now try a different case

Open the lesson and try its different practice case. Use every check in the full task. Watching alone does not mark the lesson complete.

Visual description:
Open the lesson
Try the new case
Check and revise
The full task and its requirements are in the linked lesson.