Module 1 · Descriptive Statistics · Topic 8
Match Data to Chart. The best chart depends on what you want to show and the type of data. Categorical comparisons call for bar charts. Distributions call for histograms or box plots. Relationships between two variables call for scatter plots.
Scatter Plot. A scatter plot displays pairs of quantitative values as points on an x-y plane. It is the primary tool for exploring the relationship (direction, form, strength) between two numerical variables.
Stem-and-Leaf Plots. A stem-and-leaf plot preserves individual data values while showing the shape of the distribution. The “stem” is the leading digit(s) and the “leaf” is the trailing digit. Useful for small data sets.
xbar = sum(x_i) / n — The arithmetic average of a data set.s^2 = sum((x_i - xbar)^2) / (n - 1) — Average squared distance from the sample mean with Bessel correction.Always start the y-axis at zero for bar charts (truncated axes exaggerate differences). Label axes clearly, include units, and avoid 3D effects that distort perception.
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