Question

Describe in detail the different parts of a Control Chart.

Consider a control chart that is constructed to track student attendance. Give two examples of random variation and 3 examples of assignable cause variation.

Answer 1

There are three basic components of every control chart and that are-

1 A central line which measures the average of all samples that are plotted. it is used to see the shifts or variation. it is also called process location.

2 Upper and Lower statistical control limits which are the constraints of common cause variations. They are placed equidistant from the central line. They are also called process dispersion.

3 Performance data which is plotted over a period of time . If all process values are plotted within the upper and lower control limits then it means the process is within the control. On the other hand if they go beyond the limits then it is "out of control"

Random variation also called common cause variation examples for student attendance- Bunking class, late arrival or absenteeism due as he/she woke up late. Random Variation is normal or anticipated causes.

Assignable cause variation also called special cause variation examples are- death of the child , ill due to a prolonged disease or he/she has left the school or course. Special causes are out of the blue and are not anticipated.