Accuracy, Bias & Precision

Many people are confused about statistical terms such as Accuracy and Precision. To understand the potential for improvement in testing, it is important to understand that Accuracy and Precision are different.

Accuracy is getting the “true” result. The “true” result is that obtained by strictly following the sampling and testing procedures and requirements laid down in the IWTO Test Methods and Regulations.

There are reasons why a difference between individual results can occur. However, if on average, a consistent difference exists, this is known as a Bias. Generally a Bias can be isolated to malfunctioning equipment or incorrect procedures in one laboratory which leads to that laboratory’s inaccurate results. Correct the procedure, correct the malfunction and it can be expected the Bias will disappear.

Precision is a measure of the ability to repeat a result. It can be understood by the following diagram where the cross-hair is the “true” result:

The trade must be able to expect that the results produced by AWTA Ltd and other testing laboratories are accurate and precise.