The council sends the crew a new question. "How often does a typical evening member visit?"
Comet pulls up the Q4 answers from the 9 evening members on the first two sheets, M01 to M20.
"Easy," she says. "Add them up and divide. That is the average."
Wren reads the column twice. "What do you notice about the last number?"
Comet looks. Eight answers are small, from 1 to 5. The last one is 23.
"Whoa," she says. "Somebody visited 23 times in one week?"
Nova projects the nine numbers in a row, smallest to largest. "Would you like a hint?" she asks.
"There is more than one way to find a typical value. Try three, and see whether they agree."
What is typical, and what does a pattern really prove?
This week you will find three kinds of typical value and test what a pattern can and cannot tell you.
| Evening member | Q4: Visits last week |
|---|---|
| Member A | 1 |
| Member B | 2 |
| Member C | 2 |
| Member D | 2 |
| Member E | 3 |
| Member F | 3 |
| Member G | 4 |
| Member H | 5 |
| M17 (a Commons volunteer) | 23 |
Made-up data from the Commons Count story, sorted from smallest to largest.
Only M17's ID is shown here, because the story comes back to that answer tomorrow.
The mean is the sum of the values divided by how many values there are. The mean is what most people call the average.
The median is the value with half the data smaller than it and half the data larger than it.
The mode is the value that appears most often. A data set can have more than one mode.
Finding a sum or an average of a list of numbers is a common algorithm.
| Statement | True or false? |
|---|---|
| The mean is the sum of the values divided by how many there are. | ? |
| The median has half the data below it and half above it. | ? |
| A data set can have only one mode. | ? |
| The mean, median and mode of a data set are always the same. | ? |
Strong start, data analyst. Tomorrow you will see what happens when one extreme value comes out.