Dotplot vs Comparative Dotplot
Both terms below come up in the same part of the course, and students mix them up. Here is each one defined on its own, side by side, so you can see where they part company.
Dotplot
Graphs and displays
A dotplot displays quantitative data by stacking one dot above a number line for each observation at its value.
A dotplot places every data value as a dot over its position on a number line, stacking repeats. For example, the values 3, 3, 4, and 6 would show two dots above 3 and one dot each above 4 and 6. Because each dot is one observation, you can read off the shape, center, and any gaps or outliers directly. Dotplots work best for small data sets.
Comparative dotplot
Graphs and displays
A comparative dotplot stacks two or more dotplots on the same number line so their centers, spreads, and shapes can be compared directly.
Because every dot is still one observation, a comparative dotplot compares groups without summarizing anything away, so gaps, clusters, and repeated values stay visible. For example, group A with values 4, 5, 5, 6 and group B with values 3, 5, 5, 7 share the same mean of , but B has a range of against A's . A side-by-side boxplot would also show that difference in spread, but it would hide the fact that both groups pile up at 5. Comparative dotplots work best for small data sets, since with hundreds of points the stacks grow too tall to read.