Attribute Sampling Definition, Examples & How It Works

Attribute sampling is a statistical process used during an audit to test and analyze the features of a population. This sampling process helps you know whether your processes are in control and producing the right products.

Attribute sampling is a great technique to test products for mass production. You cannot test all products, so you select a few sample products from the batch and run tests. If the sample passes the test, you say all products in the batch have passed the quality test.

The attribute sampling has binary outcomes such as “conforming” or “non-conforming,” “acceptable” or “defective,” or “accepted” or “rejected,” or “fit” or “unfit,” etc.

How Does Attribute Sampling Work?

You perform the attribute sampling during the quality inspection process. Here, you randomly select a few samples from the production process and check against the quality requirements mentioned in the quality requirements.

If the samples pass the test, you pass the complete batch. However, you will reject the complete batch if the sample does not pass the quality tests.

Methodologies of Attribute Sampling

You can use the following methodologies for attribute sampling:

• Random Sampling: In this method, auditors select sample items from the population without bias, thus ensuring that each item has an equal chance of being chosen. Random sampling helps obtain an unbiased representation of the entire batch.
• Systematic Sampling: Systematic sampling involves selecting items from the population at regular intervals. This method is efficient and practical when the items are arranged sequentially (e.g., on a production line).
• Stratified Sampling: Stratified sampling involves dividing the population into homogeneous subgroups or strata based on certain characteristics and then randomly selecting the samples from each stratum proportionate to its size. This method ensures that each subgroup is adequately represented in the sample.
• Cluster Sampling: In cluster sampling, you will divide the population into clusters or groups and randomly select entire clusters to be included in the sample. This method is useful if it is impractical or costly to sample individual items.

Example of Attribute Sampling

Now, I will share an example of the procurement process that occurred in our organization.

In our organization, you need approval based on the delegation of authority to cancel a request for quotation (RFQ). For example, any RFQ worth over 10,000 KD (Apex 33,000 USD) needs approval from the team leader.

During a yearly audit, the auditors select 100 canceled RFQs during the previous financial year to check if we have followed the correct procedures or received approval from the right authority.

They review the RFQ cancellation approval papers and submit the report to higher management.

Summary

Attribute sampling is the cornerstone of the quality assurance and control process. It helps you assess the quality of products or services. By employing sampling methodologies, you can make informed decisions, ensure compliance with approved procedures and standards, and improve continuously.