Title: Advantages and Disadvantages of Statistical Sampling
Course: PW-Course-Import-Test > Section: Module 4: Sampling and Calibration

Module 4

Like any process, statistical sampling has its advantages and disadvantages. It is essential for an engineer setting up an inspection plan to understand this in order to make an informed decision and choose the appropriate plan. The advantages and disadvantages of statistical sampling are listed below.

Advantages of Sampling

- The number of required inspectors is relatively small
- Less disruption of normal business
- Results can be obtained in a short time
- Processes can be evaluated by looking at a small number of areas
- Opportunities for improvement can be quickly identified

Disadvantages of Sampling

Sampling cannot guarantee the identification of all deficiencies in the entire lot.

- Significant deficiencies may not be in sample
- Deficiencies identified in the sampling may be an exception
- Corrective actions may be misdirected
- Little/no organization-wide info in sample

Why Not Use 100% Sampling?

One may wonder why 100% sampling of the product is not performed every time and why we have to rely on a sampling plan. There are several reasons why almost all companies shy away from 100% inspection. Let's look at situations when 100% inspection is not practical:

- When inspection/testing is destructive. There are certain inspection that may require a quality inspector to cut open a part to measure a internal dimension or perform some stress testing of the part. In such cases is one use 100% inspection there would be no product left to ship to customers.
- Some inspections are very complicated; they require complicated equipment and are time consuming. This makes the inspection costs prohibitively high.
- During 100% inspection there are chances that a quality inspector may make an error in the inspection. They may record incorrect measurement or measure the wrong dimension. When population sizes are large the probability of inspection errors is high.