Histograms and Bar Charts
Histograms display the distribution of a single numerical (continuous) variable by dividing the data range into equal-width bins and drawing bars showing the count or frequency in each bin. The x-axis represents the variable values; the y-axis represents frequency. Histograms reveal shape: symmetric, right-skewed (tail to the right), left-skewed (tail to the left), or bimodal (two peaks). For example, a histogram of exam scores for 100 students might show a bell curve centered at 75. Bar charts are superficially similar but fundamentally different: they display counts or values for categorical (non-numerical) groups. The x-axis shows categories (e.g., product types, countries); the y-axis shows frequency or value. Critically, bars in a bar chart can be reordered without changing the chart's meaning — but you cannot reorder a histogram's bins without destroying the distribution information. A key test: if your x-axis values are categorical labels, use a bar chart. If they are numerical ranges or bins, use a histogram. Histograms can also be displayed as probability density (y-axis = density instead of count) to compare distributions of different sample sizes.