A Plastic Cell Phone Case Has Been Experiencing Physical Quality

Multiple Choice

A plastic cell phone case has been experiencing physical quality control problems. That is, the clear screen does not always fit (and snap into place) on the case. The dimensions of the screen have consistently been in statistical process control (SPC) . A root cause quality initiative collected the following data about the plastic cell phone case. Analyze the width of the cell phone case using control charts and make a recommendation.
Table 1 Cell Phone Plastic Case Widths in Centimeters Data*
$\begin{array} { | c | c | c | c | c | c | c | c | } \hline & \text { Sample 1 } & \text { Sample 2 } & \text { Sample 3 } & \text { Sample 4 } & \text { Sample 5 } & \text { Sample 6 } & \text { Sample 7 } \\\hline \text { Observation } & & & & & & & \\\hline \# 1 & 6.02 & 5.92 & 5.88 & 5.99 & 6.05 & 5.94 & 6.00 \\\hline \# 2 & 5.97 & 5.83 & 5.97 & 6.08 & 6.06 & 5.96 & 5.95 \\\hline \# 3 & 5.90 & 5.87 & 5.88 & 6.08 & 5.98 & 5.99 & 5.82 \\\hline \text { Average } & 5.963 & 5.873 & 5.91 & 6.05 & 6.03 & 5.963 & 5.923 \\\hline \text { Range } & 0.12 & 0.09 & 0.09 & 0.09 & 0.08 & 0.05 & 0.18 \\\hline\end{array}$ *The sample averages and ranges helps in avoiding simple math errors and quickens the time to complete the SPC analysis.
-Given the previous results and analysis for the R-chart, one would:

A) conclude that the R-chart is in statistical process control, and proceed to develop the x-bar chart.
B) conclude that the R-chart is not in statistical process control, and search for common causes of the problem (i.e., the root cause) .
C) conclude that the R-chart is not in statistical process control, and proceed to develop the x-bar chart.
D) plot the sample means first to see if they are randomly distributed.