Accuracy is the degree of exactness or correctness whereas precision is the degree to which a measurement is reproducible. The former checks how close a measured value is to the true or accepted value while the latter checks the consistency of repeated measurements and determines how close they are to each other.
Precision and accuracy are independent of each other. A very precise measurement is not necessarily accurate and vice-versa. Good quality products should be both accurate and precise.
You will find the definition of and difference between accuracy and precision in this post. You will also find an example and diagram that will help you distinguish between these two project quality management term.
Note: You should also refer to my other articles on difference between similar Project Management Terms. They will help you answer the PMP exam questions correctly.
Accuracy and Precision Definitions
Accuracy means that the measured value is very close to true value (target or goal). Precision means that the values of repeated measurements are clustered and have very little scatter.
The above definitions are precisely accurate but they are somewhat confusing. We can understand them better by looking at their meaning in English language.
According to Merriam Webster, accuracy is “freedom from mistake or error” and “conformity of a measure to a standard or a true value”. On the other hand, Merriam Webster defines precise as “exactly or sharply defined or stated” and “minutely exact”.
Let us now go beyond the definitions and understand the difference with the help of an example and a diagram.
Difference Between Accuracy and Precision (An Example)
Accuracy measures the degree of correctness whereas precision measures degree of exactness.
Have you played Darts? I am sure you would have. The idea of the game is to hit the Bull’s Eye.
Refer to the above figure. Let us assume that it represents a dart-board. The target or goal (true value) is to put darts exactly in the center (Bull’s Eye) of the dart-board. The green circle in the above figure represents our goal.
Let us assume that we hit 4 darts and all of them landed inside the green circle. We can say that we met our goal. Or in other words we can say we were Accurate (Correct).
Let us assume that we hit another 4 darts and all of them landed in the blue circle. All the 4 darts were very close to each other. We did not meet our goal but there was hardly any space between the darts. We can say that there was very little scatter. Or in other words we can say we were Precise (Exact).
Green circle darts are Accurate but not Precise (too much of Scatter). Blue circle darts are Precise but not Accurate (not hitting the goal).
- an accurate measurement may not be precise
- a precise measurement may not be accurate.
A project manager along with other stakeholders (who are providing the requirements) must determine required level of accuracy and precision for measurements. Both are important for the project.
In order to use these terms accurately, you can start by inculcating them in your daily life. e.g. if your goal is to become PMP certified then you should be precise. You should define a time target for yourself.
All the best.