In: Statistics and Probability
An insurance company samples claim forms for errors created by its employees as well as the amount of time it takes to process a claim. Repeated samples of six claims are taken over a twenty day period. In the table below are the average times and ranges for each of the samples.
X bar range
24.3 2.8
23.5 2.5
27.2 3.2
27.5 5.8
25.8 3.2
23.5 4
24.9 4.1
20.6 3.4
22.7 7.4
26 3.7
25.5 4.2
23.3 2.5
24.1 3
25.6 2.9
27.1 3.5
24.3 3.0
26.1 3.6
25.2 2.9
26.1 4.2
28.3 4.5
Construct and x bar and R chart. Comment on the operation of the insurance claims department based on this information.
To construct the Xbar and R chart we will be going in a step by step manner:
Calculate Control Limits:
Calculate the R chart limit:
as sample size 6 is below 7, then D3 will be 0 and we have obtained the value from the table of D4 which is 2.004
Now for the A2, we again have taken help of the table and the value is 0.483
Now we will calculate the data for X bar and R chart
Control Limits, X-bar Chart | Control Limits, R Chart | ||||||||||
Sample | Sample Mean | Range | LCL | UCL | Mean | LCL | UCL | R-bar | Range | ||
1 | 24.3 | 2.8 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 2.8 | ||
2 | 23.5 | 2.5 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 2.5 | ||
3 | 27.2 | 3.2 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.2 | ||
4 | 27.5 | 5.8 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 5.8 | ||
5 | 25.8 | 3.2 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.2 | ||
6 | 23.5 | 4.0 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 4.0 | ||
7 | 24.9 | 4.1 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 4.1 | ||
8 | 20.6 | 3.4 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.4 | ||
9 | 22.7 | 7.4 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 7.4 | ||
10 | 26.0 | 3.7 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.7 | ||
11 | 25.5 | 4.2 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 4.2 | ||
12 | 23.3 | 2.5 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 2.5 | ||
13 | 24.1 | 3.0 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.0 | ||
14 | 25.6 | 2.9 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 2.9 | ||
15 | 27.1 | 3.5 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.5 | ||
16 | 24.3 | 3.0 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.0 | ||
17 | 26.1 | 3.6 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 3.6 | ||
18 | 25.2 | 2.9 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 2.9 | ||
19 | 26.1 | 4.2 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 4.2 | ||
20 | 28.3 | 4.5 | 23.28324 | 26.87676 | 25.08 | 0 | 7.45488 | 3.72 | 4.5 | ||
Mean | 25.08000 | 3.72 | 3.72 | ||||||||
Factors | |||||||||||
n | A2 | D3 | D4 | ||||||||
6 | 0.483 | 0 | 2.004 | ||||||||
The X bar chart will be like below:
And the R chart will be like below:
From the X bar chart, we can see that the sample number 4,8,9,20 has breached the range limit. But in R chart we can safely say that all the range values are within the limits.
Thanks !!