Module 1 · Descriptive Statistics · Topic 7
Why Visualize Data?. Visualizations reveal patterns, trends, and outliers that raw numbers alone might hide. A good chart communicates the story in the data quickly and clearly.
Common Chart Types. Histograms show frequency distributions of quantitative data. Bar charts display counts or percentages for categorical data. Box plots summarize the five-number summary. Dot plots show individual data points along a number line.
Histograms vs Bar Charts. Histograms have adjacent bars (no gaps) because the x-axis is a continuous scale. Bar charts have gaps between bars because each bar represents a separate category.
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.To show the distribution of test scores for 200 students, use a histogram. To compare the number of students in each major, use a bar chart. To compare score distributions across three classes, use side-by-side box plots.
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