X-bar Chart for Etch Rate Data
Tim Matis
Last compiled on March 04, 2026 at 11:08 AM - CST
1 Introduction
This is a document that shows an X-bar chart for Etch Rate data.
There are 20 subgroups of size \(n=5\)
that have been collected over time. We are going to use the package
qcc in doing so.
#install.packages("qcc")
library(qcc)We load the dataset EtchRateRetroData.csv
df <- read.csv("https://raw.githubusercontent.com/tmatis12/datafiles/refs/heads/main/EtchRateRetroData.csv", header = FALSE)2 X-bar Chart
We would like to create an X-bar chart for this data.
2.1 Formulas for X-bar Chart
The X-bar chart has the following control limits:
\[ UCL = \bar{\bar{x}} + 3\frac{\hat{\sigma}}{\sqrt{n}} \]
\[ CL = \bar{\bar{x}} \]
\[ LCL = \bar{\bar{x}} - 3\frac{\hat{\sigma}}{\sqrt{n}} \]
2.2 QCC Output
The qcc object for the X-bar chart is given below:
xbar <- qcc(data = df, type = "xbar", nsigmas = 3)
3 Complete R Code
#install.packages("qcc")
library(qcc)
df <- read.csv("https://raw.githubusercontent.com/tmatis12/datafiles/refs/heads/main/EtchRateRetroData.csv", header = FALSE)
xbar <- qcc(data = df, type = "xbar", nsigmas = 3)