Definition: The mean is the average of a data set, found by adding all the values and dividing the sum by how many values there are.
What is the mean?
The mean is the fair-share value. If every data point were leveled out to the same number, that number would be the mean.
How do you compute it?
Add the data, then divide by the count. Mathbot clocked these lap times in seconds: 41, 38, 47, 44, 40.
- Sum: 41 + 38 + 47 + 44 + 40 = 210
- Count: 5
- Mean: 210 / 5 = 42 seconds
Why is it a balance point?
On a dot plot, the mean is where the data would balance. Deviations from it cancel out: -1, -4, +5, +2, -2 add to 0.
What does an outlier do?
The mean is sensitive to extremes. Replace 47 with 147 and the sum becomes 310, so the mean jumps to 62, even though four of the five laps barely changed.
What is the common mistake?
Dividing by the wrong number. If a value appears twice, count it twice. Also, the mean is not always in the data set, and it may not be a whole number.