Normal Variation

Question 1

What is normal variation?

Answer 1

All processes experience normal random variation. This is often modeled with a bell-shaped curve and can be described with statistical data parameters including the mean, median, range and standard deviation.

Question 2

When do you use SPC analysis?

Answer 2

You will need to determine the pattern of variation. Once the variation has become normal variation, you can begin to control the process.

Question 3

How is normal variation represented?

Answer 3

In a bell shaped curve which is a symmetrical distribution that has a high center peak and with upper and lower edges that approach zero.

Question 4

What is another name for a bell shaped curve?

Answer 4

Gaussian distribution

Question 5

Who is the Gaussian distribution named after?

Answer 5

Carl Gauss the father of the science of statistics

Question 6

What is the MEAN

Answer 6

this is the average value of all the items in a data set. Meaning you add all the values together and then divide by the number of items in the data set. The result is your mean.

Question 7

What is range?

Answer 7

This is the span from the smallest value to the largest value in the data set.

Question 8

Standard Deviation

Answer 8

This is a statistical measure of the typical spread of the data. It starts with the difference of each value from the mean value, which is called a deviation. It then squares those deviations, determines the average of those and then takes the square root of that number.

Question 9

What can a standard deviation be used to predict?

Answer 9

The standard deviation for a normal curve can be used to predict the percentage of values in the data set that will fall within a span

Question 10

What is 3+- standard deviations

Answer 10

in SPC is the span from minus 3 standard deviation to plus 3 standard deviations. This span will contain 99.73% of all the data values in the data set. This range was used by Walter Shewhart when first developing SPC control charts.

Question 11

What does a normal distribution tell you?

Answer 11

When your data set for a process parameter is represented by a normal distribution, you know you are dealing with random variation. This type of process is an ideal candidate for statistical process control.