Read Percentage Claims with Their Baselines

Distinguish relative change, percentage points, and unsupported explanations.

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Find the starting value and denominator. A change from 4% to 2% is a decrease of 2 percentage points and 50% relative to the starting rate. Neither calculation by itself proves why the change occurred.

Worked example

A headline can be numerically correct yet incomplete if it omits the baseline, time period, or relevant comparison.

Invented Report

A workshop newsletter says the defect rate fell from 6% to 3% after a new process began. It calls this a '50% reduction.' It does not report sample sizes, selection methods, or a comparison workshop.

1. What is the decrease in percentage points? 50 percentage points 3 percentage points 2 percentage points

2. What is the relative percentage decrease? 3% 100% 50%

3. Which statement gives both useful measures? The rate fell from 6% to 3%, a 3-point or 50% relative decrease The rate fell by 50 percentage points The rate became negative

4. Does the before-and-after comparison alone prove the new process caused the change? Yes, later always means caused by No, other changes may also explain it Yes, percentages prove every explanation

5. Which missing detail matters for assessing the reliability of the rates? Only the headline's color Only the company logo The number and selection of items checked in each period

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