Bar Chart
Bar chart from worksheet columns: frequency, mean, or sum per category
Anatomy of a Bar Chart
A bar chart draws one vertical bar per category, the height of which expresses a numeric value. It is the most straightforward tool to compare discrete quantities — the eye translates bar length into magnitude almost without error.
Category (X axis): A discrete level for which a bar is drawn — e.g. "Shift A / B / C", "Defect type", "Supplier". The category list is finite and named, not numerically ordered.
Value (Y axis): The quantity the bar represents. Three options: (1) a pure frequency count of the category ("how often does it appear?"), (2) the mean of a numeric column per category, (3) the sum of a numeric column per category.
Grouping: When a second categorical column is supplied, each X-category becomes a bundle of bars (or a stacked bar) — each subgroup in its own color. This makes effects such as "defect type × shift" or "supplier × plant" comparable at a glance.
Grouped vs. stacked: "Grouped" places subgroups side-by-side — good for direct comparison. "Stacked" piles them — good for seeing the per-category total while still showing the split.
Bar charts are suited to comparing categories on a single metric — such as "average cycle time per shift" or "frequency of defect types". For a variant sorted by frequency with a cumulative line, use a Pareto chart. For continuous data with a binned axis, the histogram is the right tool.
Pitfalls
Y axis does not start at zero: Truncating the Y axis (e.g. starting at 90 instead of 0) makes differences look more dramatic than they are. This is one of the most common — and most misleading — manipulations with bar charts; length comparisons require the axis to start at 0.
Too many categories: More than 10–15 categories become visually overwhelming. Sort by frequency (→ Pareto chart) or group small categories into "Other".
Mean without spread: A bar shows only the mean (or sum) — within-category spread is invisible. If heterogeneity is plausible, complement with a boxplot or individual-value plot.
Confusing frequency with mean: When a Y column is set, the bar shows the mean (or sum) of Y per category, not the count. Check the axis label and the stats table so the chart is not misread.
Stacked bars with many subgroups: Stacked bars are hard to read when subgroups are very uneven in size or when there are more than 4–5 of them. Prefer a mosaic chart or a heatmap in such cases.
Examples
This module ships with the following example datasets — load any of them in the app with a single click.