Key takeaway: A dot plot is a data display that puts one dot above a number line for every value in a data set, stacking dots when values repeat, so clusters, gaps and outliers are easy to see.
Grade 66.SP.B.4Statistics and Data
Definition of Dot Plot
A dot plot shows each data value as a dot above a number line. When a value appears more than once, the dots stack in a column, so a tall stack means a common value.
Because every piece of data is visible, you can read the count of any value, spot where the data cluster, notice gaps between groups, and see any value far from the rest. It works best for small to medium sets of numbers with many repeats. To build one, draw an evenly spaced number line that covers the data, and then place one dot per value, directly above its position.
Formula and notation
Each dot stands for one observation. Counting every dot gives the total number of values, \(n\):
\[n = \text{number of dots}\]
The axis needs a label with units, such as “minutes of practice”, and a title tells what was measured.
Key facts
- The tallest stack marks the mode, the value that occurs most often.
- A wide empty stretch on the axis shows a gap in the data.
- Dots must be the same size and sit evenly above their value.
- Counting all the dots tells you how many data values were collected.
Dot Plot example
Twelve students recorded their practice time in minutes: 20, 20, 25, 25, 25, 30, 30, 35, 35, 35, 35, 60. Describe the dot plot.
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Count the dots at each value: 20 has 2, 25 has 3, 30 has 2, 35 has 4, 60 has 1. The total is \(2 + 3 + 2 + 4 + 1 = 12\).
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The tallest stack is at 35, so the mode is 35 minutes.
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The data cluster between 20 and 35, then there is a gap from 40 to 55, and one value at 60 stands apart.
The mode is 35 minutes, most students practiced 20 to 35 minutes, and 60 is far from the rest.
Common mistake
Watch out
Isla counts the labels on the axis, 9 of them, and says there are 9 students.
Why it is wrong
The axis labels only mark positions. Each student is one dot, so count the dots: 12 students in all. Some labels, like 40 and 45, have no dots at all.
Related terms and lessons
Browse the glossary: A–Z list · Grade 6 vocabulary · Statistics and Data