Mistake Master · AP Statistics · Unit 1 · Step-Through Animation
Four Ways a Survey Breaks, and They Break Different Links
You'll learnto name which link of the chain from population to recorded answer a survey broke, and to say which way that break pushes the estimate and why.
A survey runs down a chain: a population, a frame of everyone who could be picked, the people actually selected, the ones who answer, and the answers as recorded. 240 residents, 58.3% of whom ride the bus weekly. Sample from the car registry and the frame is missing riders — its target is 30.8%. Run an open web poll and nobody is selected at all; the 80 who choose to answer are 87.5% riders. Phone the selected on a weekday and the riders are out; the people you can reach are 41.2% riders. Ask "do you do your part by riding the bus" and everyone answers, but the recorded rate town-wide is 77.1%. Four numbers, two too high and two too low, and not one of them moves when the sample grows.
One survey drawn as five stages stacked top to bottom. The bar is how many people are left at that stage; the track on the right is what percentage of them ride the bus.
The question
Four surveys of the same town return four different answers. Which link did each one break?
Watch for
The row where the marker leaves the dashed rule and never comes back. A break moves it and holds it there; chance only jostles it once.
Mistake Master