Graphing Rules

The following rules are for vertical bar charts. For horizontal bar charts, change "vertical" to "horizontal" and "horizontal" to "vertical" in these rules.

Put a title at the top of the graph.
The vertical axis scale should be uniform and start at zero.
Use horizontal grid lines.
Each bar should be labeled by what it represents.
Label the vertical axis “Frequency” or “Count”.

The horizontal axis label should describe the qualitative variable that the bar chart represents. If the individual bar labels are descriptive enough, a horizontal axis label is not necessary.

Example of a Qualitative Bar Chart

Dot Plot

Put a title at the top of the graph.
The horizontal axis scale should be uniform.
Make sure the horizontal axis scale extends from the lowest value, or just below the lowest value, to the highest value or just above the highest value.
The horizontal axis label should describe the quantity being measured, including the units, if any.
A vertical axis is not needed.

Example of a Dot Plot

Histogram

The following rules are for vertical bar charts. For horizontal bar charts, change "vertical" to "horizontal" and "horizontal" to "vertical" in these rules.

Put a title at the top of the graph.
The vertical axis should be uniform and start at zero.
Use horizontal grid lines.
Mark the horizontal scale using one of the following four methods.
- Label the left edge of each bar with the corresponding lower class limit.
- Label the right edge of each bar with the corresponding upper class limit.
- Label the middle of each bar with the corresponding class midpoint.
- Label the edges of the bars with the corresponding class boundaries
The horizontal axis label should describe what is being measured and include the units if there are any.
Label the vertical axis “Frequency” or “Count”.

Example of a Histogram

Single Horizontal Box Plot

Put a title at the top of the graph.
The horizontal axis scale should be uniform.
Include vertical grid lines.
Make sure the horizontal axis scale extends from the lowest value, or just below the lowest value, to the highest value or just above the highest value.
The label for the horizontal axis should describe the quantity being measured, including the units if any.
A vertical axis is not needed.

Example of a Single Horizontal Box Plot

Side-by-side Horizontal Box Plot

Put a title at the top of the graph.
The horizontal axis scale should be uniform.
Use vertical grid lines
Make sure the horizontal axis scale extends from at or just below the lowest value, to at or just above the highest value.
The label for the horizontal axis should describe the quantity being measured, including the units if any.
A vertical axis is not needed.
Each box plot represents a different data set and should be labeled for the data set it represents.

Example of a Side-by-side Horizontal Box Plot

Time Series

Put a title at the top of the graph.
Both axis scales should be uniform.
Use both horizontal and vertical grid lines.
The horizontal scale should extend from at or just below the lowest time-value to at or just above the highest time-value.
The vertical scale should extend from at or just below the lowest non-time value to at or just above the highest non-time value.
The horizontal axis label should describe the time being measured, including the units if any.
The vertical axis label should describe the quantity being measured at each time interval, including the units if any.

Example of a Time Series

Scatter Diagram

Put a title at the top of the graph.
Both axis scales should be uniform.
Use both horizontal and vertical grid lines.
The horizontal scale should extend from at or just below the lowest x-value to at or just above the highest x-value.
The vertical scale should extend from at or just below the lowest y-value to at or just above the highest y-value.
The horizontal label should describe what the x-values are measuring, including the units if any.
The vertical label should describe what the y-values are measuring, including the units if any.

Example of a Scatter Diagram

Normal Probability Plot

To create a normal probability plot in Minitab, do the following.

Click on the "Stat" tab.
Choose "Basic Statistics".
Next choose "Normality Test".
Click in the box to the right of "Variable:".
Choose the variable you want to plot from the box on the left side of the window.
Click in the circle next to Ryan-Joiner.
Click on the "OK" button.
Make sure the label on the horizontal axis describes the variable being plotted.
The "Normal" subtitle may be deleted.