Idea 22of 22Builds onCompare shares, not counts
A sample predicts the group
How can a sample tell you about everyone?
Today you'll discover
- how a sample's share carries to the school
- how to work out the prediction
- when not to trust it
Think first6 of the 24 asked want a court
6 of the 24 students asked want a court. About how many of all 240?
Decide first, then press Next. Watch the short sample bar stretch to the school's length.
Two bars: the sample, 6 of 24 want a court, and the school of 240 with its part unknown. Each whole is drawn to the same scale, the sample a tenth as long. Then both are drawn the same length, and a dashed part on the school's bar matches the sample's part: about 60. Marks every 10% show both at 25%.
See the whole ideathe big idea and the key word, in one place
The big idea
A fair sample's share is a prediction for the population: 6 of 24 suggests about 60 of 240.
Keep the share
Find the sample's share, then take the same share of the population.
- sample6 of 24
- share1 in 4, 25%
- schoolabout 60 of 240
Easy to get wrongA prediction is close, not exact. Another fair sample might suggest 55 or 65, and that is normal variation.
Key word
- prediction
- a careful guess about the whole population, made from a fair sample
Ready to use it?
- Use a sample's relative frequency to predict for the population.