Comet spreads the member list across a table. "There are 120 members," she says. "We ask every single one. No exceptions!"
Keeper Ines laughs softly. "Some members only come once a month. You might wait a long time."
Wren taps the list. "What do you notice? We may only hear from some of them. Maybe 40, if the week goes well."
"Is that still useful?" Comet asks.
Nova projects two circles on the wall, one full and one with a few dots. "Would you like a hint?" she asks. "One is called a census. The other is called a sample."
Wren looks at you. "Data analyst, which one will Commons Count be?"
A census counts everyone in a group.
The U.S. census happens every ten years. It counts every person living in the country.
A survey such as the American Community Survey goes to a sample instead: about 3.5 million addresses.
A sample asks some members of a group in place of everyone.
In a random sample, each person who answers stands for many others.
The Census Bureau picks the addresses for its survey at random.
The crew expects about 40 of the 120 members to answer during the survey week. This number is made up for the story.
40 out of 120 is one out of every three members.
If those 40 were a random sample, each answer would stand for about 3 members.
Whether the 40 really are like the other 80 is a question the crew will come back to.
| Statement | True or false? |
|---|---|
| A census counts everyone in a group. | ? |
| The U.S. census happens every year. | ? |
| In a random sample, each person who answers stands for many others. | ? |
| The Census Bureau picks addresses for its survey at random. | ? |
| If 40 of 120 members answer, Commons Count is a census. | ? |
Clear thinking. Tomorrow in Count Lab you draft the survey questions.