Causes of Errors

Even if we want to make "same" products, they are not same.

There are some causes of errors. In my experience, I did not check all causes to solve problems of errors.

Links Between Kinds of Errors and Causes

There are accidental errors and systematic errors . In many cases, I think the causes are systematic errors.

I think accidental errors for the errors of repeated measurement. In this case, the approximation of normal distribution goes very well.

Cause of Errors

The cause of errors has a structure of level.

Repeatability of Measurement

If we measure a same sample in a same way, this error is not zero in many cases.

Difference of Measurement Machine

The output of different machine is often different even if the sample is same.

If the methods of the measurement are different the error is larger.

Sampling

Sampling is not easy if the phenomenon we want to measure is unstable.

Process

In Process Analysis for Abnormal Condition , this error is often important. The small difference of process could be a large error.

Person

The difference of the persons could be the cause.

One of the differences of the unevenness is personal abilities.

The other is the difference of the process of each person. For this problem, normalization is a popular solution.

Division of Errors

If we understand the size of each error, decision making is easier. Standard Deviation is an index of errors.

If there are some causes of errors, calculation of the index is not easy. An application of Design of Experiments has logic to divide errors mathematically. (This site does not explain this logic because the explanation needs many pages.)