Difference between Accuracy and Precision

Many people get confused between the two terms Accuracy and Precision.

Actually, these are not only industrial terms, but also use in our daily services.

Let’s understand the difference between Accuracy and Precision with one simple example,

EXAMPLE 1: (REAL-TIME SCENARIO)

For instance, You walk daily 3 km. And you set your target to complete that entire path in 20min.

Case 1

On the first day, you completed your target in 20:01 min, second day 20:03 min, and the third day 20:05 min.

These readings are near to the true value of 20:00 which means readings are Accurate.

Case 2

The same exercise was performed three days and you noted reading 21.45, 21.40, and 21.55 respectively

Here, readings are very near to each other, but not the same as true value. It means reading is nearest to successive reading called precise reading.

Let’s take another example,

EXAMPLE 2 : (PRACTICAL SCENARIO)

In the practical session, you are measuring the voltage through a circuit using a Voltmeter with an accuracy of 0.1 V. And the true value of the voltage is 230 V. The instrument is within accuracy if the voltage is in between 229.9 to 230.1 volts.

Now,

Case 1

You get to read as 230.31, 230.30, 230.29, 230.32, and 230.30

In this case, we can observe that all five readings are nearest to each other, but they are not in range of the voltmeter

From this, we can conclude that all the readings are precise but not accurate.

Case 2

You get reading as 230.01, 229.99, 230.03, 230.05, and 229.99

In this case, we can observe that all five readings are in the Accuracy range of voltmeter and nearest to the true value

From this, we can conclude that all the readings are accurate but not precise.

Case 3

You get reading as 230.01, 230.02, 230.02, 230.01, and 230.02

In this case, we can observe that all five readings are nearest to each other as well they all are in the Accuracy range of voltmeter and nearest to the true value

From this, we can conclude that all the readings are precise and accurate.

Case 4

You get reading as 230.05, 229.98, 230.25, 230.39, and 229.81

In this case, we can observe that all five readings are neither nearest to each other,nor they all are in the Accuracy range of the voltmeter and nearest to the true value

From this, we can conclude that all the readings are not precise and accurate.

Definition of Accuracy and Precision

Accuracy: it is defined as how close a value to its True Value.

Precision: It is defined as how repeatable a measurement is.

Comparison of Accuracy and Precision

Accuracy:

Accuracy is closeness with the true value of the quantity being measured
Measurement can be accurate but not necessarily precise.
It can be determined with a single measurement
Accuracy may be affected by systematic error
Accurate values have to be precise in most cases

Precision

Precision is a measure of the reproducibility of the measurement
Measurement can be precise but not necessarily accurate
It needs several measurements to be determined
Precision may be affected by random error
The precise value may or may not be accurate

Difference between Accuracy and Precision