Bar Charts are used for discrete or categorical data, where each bar represents a distinct group; a critical feature is the presence of gaps between bars to signify that the categories are separate.
Histograms are used for continuous data, where the x-axis represents intervals (bins) of a numerical variable; unlike bar charts, the bars in a histogram must touch to show the continuous nature of the scale.
Line Graphs are ideal for showing trends over time or changes across a continuous independent variable, where data points are connected by lines to highlight the direction of change.
Pie Charts represent data as proportions of a whole (), where the size of each 'slice' corresponds to the percentage or frequency of a specific category.
Scattergrams (or scatter plots) are used to display the relationship between two co-variables in correlational research, where each point represents one participant's score on both variables.
In a scattergram, the pattern of dots indicates the direction (positive or negative) and strength (how closely the dots form a line) of the correlation.
Choosing the correct display depends entirely on the level of measurement and the nature of the data (discrete vs. continuous).
| Feature | Bar Chart | Histogram | Line Graph |
|---|---|---|---|
| Data Type | Categorical / Discrete | Continuous (Intervals) | Continuous (Trends) |
| Visual | Gaps between bars | Bars touch | Points connected by lines |
| Purpose | Comparing groups | Showing distribution | Showing change over time |
Always ensure every graph has a fully descriptive title that mentions both the independent and dependent variables (e.g., 'A graph to show the effect of X on Y').
Label both the x-axis and y-axis clearly, including units of measurement where applicable (e.g., 'Time in seconds' or 'Score out of 50').
Check the scale of your axes; intervals should be equal and consistent to avoid distorting the data's appearance.
A common mistake is using a bar chart for continuous data; remember that if the data can be any value on a scale (like height or time), a histogram or line graph is usually required.
