Concept:
P-chart (Proportion or Fraction Defective Chart)
- It is used to monitor and control the fraction produced in a process that is defective or non-conforming.
- It follows a binomial distribution.
- This chart is best suited in cases where inspection is carried out to classify articles as either excepted or rejected.
\(Control\;limits = \bar p \pm 3 \times \sqrt {\frac{{\bar p\;\left( {1 - \bar p} \right)}}{n}} \)
Calculation:
Given:
The average proportion, \(\bar p\) = 0.12
Size, n = 100
\(Control\;limits = \bar p \pm 3 \times \sqrt {\frac{{\bar p\;\left( {1 - \bar p} \right)}}{n}} \)
Upper Control Limit (UCL) is given by :
\(Upper \:control\;limit = 0.12 + 3 \times \sqrt {\frac{{0.12\;\left( {1 - 0.12} \right)}}{100}} \)
\(Upper \:control\;limit = 0.12 + 3 \times \sqrt {\frac{{0.12\;\left( 0.88 \right)}}{100}} \)
∴ UCL = 0.21
