A c-chart is a control chart used when the count of defects or occurrences has to be controlled. Therefore the lower and upper control limits of the C-chart need to be calculated and the two-sigma control limits have to be evaluated.

Thus z=2

Using the following formula the UCL and LCL are calculated:

UCL=c-bar +z c-bar =3+23=3+3.4641 = 6.464

LCL= c-bar-z c-bar =3-23 =3-3.4641 0

The LCL value has been considered as zero, since the derived value is negative. Thus the two-sigma control limits, the UCL and LCL has been derived as 6.464 and 0.0006.464 and 0.000 respectively.

A client who has planned a trip to Dallas has six errors in her itinerary. The derived upper and lower control limits are 6.464 and 0.000 respectively, which means that six errors are within the control limits of 6.464 and 0.000 and hence it can be concluded that the itinerary is within statistical control.

UCL = c_bar + z*sigma_c

LCL = c_bar - z*sigma_c

c_bar = average defects per item

sigma_c = sqrt(c_bar)

z = sigma limit

In this case

c_bar = 5

sigma_c = sqrt(5) = 2.23

z= 3

UCL =5 + 3*2.23

= 11.69

LCL = 5 - 3*2.23

= 0 (negative is not possible)

Question is the following:

Graphic (draw) a c- chart using the information above.