Question

Problem 3-2. A Quality Control Decision
Glucose Control Values
Day Low High
1 86 215
2 82 212
3 83 218
4 87 214
5 85 220
6 81 217
7 88 223
8 83 224
9 82 217
10 85 222

1. Calculate the mean and standard deviation for the
above dataset.
2. Plot these control data by day (one graph for each
level, x-axis = day, y-axis = concentration). Indicate
the mean and the upper and lower control limits
(mean ±2 standard deviations) with horizontal lines
(see Fig. 3-28).
3. You are working in the night shift at a community
hospital and are the only person in the laboratory.
You are running glucose quality control and obtain
the following:
Low control value = 90; High control value = 230
Plot these controls on the process control chart
(Levey-Jennings) you created above.
4. Are these values within the control limits?
What do you observe about these control data?
5. What might be a potential problem?
6. What is an appropriate next step?

Answer 1

1) The mean for low glucose control values is,

Mean = (86+82+83+87+85+81+88+83+82+85)/10

Mean = 84.2

Standard deviation is,

= Square root of summation of (x - ×')/n

= 2.227

The mean for high glucose control value is,

= (215+212+218+214+220+217+223+224+217+222)/10

= 218.2

Standard deviation is,

= Square root of summation of (x - x')/n

= 3.789