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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.
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Put a title at the top of the graph.
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The vertical axis scale should be uniform and start at zero.
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Use horizontal grid lines.
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Each bar should be labeled by what it represents.
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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
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Dot Plot
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Put a title at the top of the graph.
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The horizontal axis scale should be uniform.
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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.
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The horizontal axis label should describe the quantity being measured, including the units, if any.
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A vertical axis is not needed.
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Example of a Dot Plot
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Histogram
The following rules are for vertical bar charts. For horizontal bar charts, change "vertical" to "horizontal" and "horizontal" to "vertical" in these rules.
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Put a title at the top of the graph.
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The vertical axis should be uniform and start at zero.
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Use horizontal grid lines.
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Mark the horizontal scale using one of the following four methods.
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Label the left edge of each bar with the corresponding lower class limit.
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Label the right edge of each bar with the corresponding upper class limit.
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Label the middle of each bar with the corresponding class midpoint.
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Label the edges of the bars with the corresponding class boundaries
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The horizontal axis label should describe what is being measured and include the units if there are any.
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Label the vertical axis “Frequency” or “Count”.
Example of a Histogram
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Single Horizontal Box Plot
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Put a title at the top of the graph.
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The horizontal axis scale should be uniform.
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Include vertical grid lines.
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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.
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The label for the horizontal axis should describe the quantity being measured, including the units if any.
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A vertical axis is not needed.
Example of a Single Horizontal Box Plot
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Side-by-side Horizontal Box Plot
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Put a title at the top of the graph.
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The horizontal axis scale should be uniform.
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Use vertical grid lines
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Make sure the horizontal axis scale extends from at or just below the lowest value, to at or just above the highest value.
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The label for the horizontal axis should describe the quantity being measured, including the units if any.
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A vertical axis is not needed.
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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
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Time Series
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Put a title at the top of the graph.
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Both axis scales should be uniform.
- Use both horizontal and vertical grid lines.
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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.
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The horizontal axis label should describe the time being measured, including the units if any.
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The vertical axis label should describe the quantity being measured at each time interval, including the units if any.
Example of a Time Series
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Scatter Diagram
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Put a title at the top of the graph.
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Both axis scales should be uniform.
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Use both horizontal and vertical grid lines.
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The horizontal scale should extend from at or just below the lowest x-value to at or just above the highest x-value.
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The vertical scale should extend from at or just below the lowest y-value to at or just above the highest y-value.
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The horizontal label should describe what the x-values are measuring, including the units if any.
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The vertical label should describe what the y-values are measuring, including the units if any.
Example of a Scatter Diagram
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Normal Probability Plot
To create a normal probability plot in Minitab, do the following.
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Click on the "Stat" tab.
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Choose "Basic Statistics".
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Next choose "Normality Test".
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Click in the box to the right of "Variable:".
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Choose the variable you want to plot from the box on the left side of the window.
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Click in the circle next to Ryan-Joiner.
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Click on the "OK" button.
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Make sure the label on the horizontal axis describes the variable being plotted.
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The "Normal" subtitle may be deleted.
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Example of a Normal Probability Plot
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