Section 1
Dot Plots: Construction and Analysis
Property
A dot plot displays the frequency of quantitative data along a number line. It is ideal for smaller data sets.
To construct a dot plot, order the data from least to greatest and place exactly one dot directly above its value on the number line. When values repeat, the dots must be stacked perfectly vertically.
Dot plots allow you to easily identify the shape of the data, including:
- Peaks: The value(s) with the tallest stack of dots (the mode).
- Clusters: Groups of data points gathered closely together.
- Gaps: Empty intervals on the number line.
- Outliers: Individual values that stand far away from the rest of the data.
Examples
- Constructing and Stacking: Data set is {7, 3, 5, 3, 7, 5, 3}. Order it first: 3, 3, 3, 5, 5, 7, 7. Place three dots above the 3, two dots above the 5, and two dots above the 7.
- Stacking Error: A student plots the value 4 twice but places the second dot slightly to the right instead of directly above the first. This makes it look like a new data value near 4.5 exists. Dots must be stacked straight up.
- Analyzing Features: Looking at a dot plot of "pets owned," you see a peak at 1, a cluster from 0 to 2, a gap at 4, and an outlier at 7.