The Psychology of Quality and More

A Toolbook for Quality Improvement and Problem Solving (contents)

Line Graph: How to do it

The Quality Toolbook > Line Graph > How to do it

When to use it | How to understand it | Example | How to do it | Practical variations

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How to do it

1. Identify the objective of the graph and what decisions may be made from its use. Typical objectives include measuring progress towards a target or variation within specified limits.
    
2. Decide what to measure and what lines to plot on the graph to be able to make the requisite decisions. This may include plotting additional lines such as goal or limit lines.
    
3. Define the axes and scales on the graph such that the line will fill the graph area without overshooting. Sometimes this cannot be done until the measurements have been made.
   The general rule for deciding which is the X-axis (horizontal) and Y-axis (variable) is that 'when something is changed on the X-axis, then as a result something changes on the Y-axis'.
    
4. Take the measurements, recording them either directly onto the graph or into a table. If someone else is to do this, ensure they are trained and able to do it. If appropriate, do a pilot run to check that the process works.
    
5. Plot the points on the graph. If there are multiple lines, make sure each line can be clearly identified. Label the graph with axis titles, scales and other data, such as details of the process measured, dates, etc.
    
6. Interpret the graph and take appropriate action.

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