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Precision
Precision
Precision refers to the degree of consistency or reproducibility of a measured value. It indicates how closely multiple measurements of the same quantity agree with each other. A highly precise measurement will have very little variability between individual measurements.
Example: Suppose you are measuring the length of an object using a ruler that is divided into millimeters. If you perform multiple measurements and consistently obtain values such as 10.2 mm, 10.3 mm, and 10.1 mm, the measurements are considered to be precise because they exhibit very little variation.
Accuracy:
Accuracy:
Accuracy describes how close a measured value is to the true or accepted value of a quantity. It indicates the absence of systematic errors or biases in the measurement process. An accurate measurement represents a small deviation from the true value.
Example: Let's say a standard reference length for an object is known to be 100.0 cm. If upon measuring the object using an accurate instrument, you obtain 99.8 cm, your measurement would be considered accurate because it is very close to the true value.
Accuracy Vs Precision
Accuracy Vs Precision
Scenario 1: A precise but not accurate measurement:
Scenario 1: A precise but not accurate measurement:
A precise, but not accurate measurement is similar to an archer hitting near the same spot on a target, but the spot is not near the bullseye.
If you measure the length of an object repeatedly using a faulty ruler that is shifted by 2 mm, and consistently get 98 mm, 99 mm, and 100 mm, your measurements are precise (consistent with each other), but they are not accurate because they are systematically shifted from the true value.
Scenario 2: An accurate but not precise measurement:
Scenario 2: An accurate but not precise measurement:
If you measure the length of an object using a faulty ruler that randomly jumps within a range of 5 mm, and obtain values such as 90 mm, 106 mm, and 95 mm, your measurements are not precise (vary significantly), but the average value is close to the true value, making it accurate.
A accurate, but not precise measurement is similar to an archer hitting near the bullseye, but each individual arrow is spread apart. But the average of the arrows would be at the center of the bullseye.
Scenario 3: A Precise and Accurate measurement
Scenario 3: A Precise and Accurate measurement
An accurate and precise measurement is similar to an archer hitting the bullseye each time with each arrow only being slightly apart.
If you measure the voltage of a 12V battery and get a reading of 12.01 V, 12.00, 11.99 V. Your measurements are both accurate and precise. Each individual measurement is close to each other, and close to the true value of the battery (12V)
Scenario 4: A Neither Precise or Accurate Measurement
Scenario 4: A Neither Precise or Accurate Measurement
If you measure the voltage of a 12.00 V battery and get a reading of 13.3 V, 11.0 V , 14.2 V. Your measurements are neither accurate or precise. Each individual measurement is far apart from each other, and the average measurement is not close to the true value of the battery.
A measurment that is neither precise or accurate is similar to an archer hitting a target with each arrow away from the bullseye, and not near each other.
Concept Summary:
Concept Summary:
In summary, precision relates to the consistency of measurements, while accuracy relates to the correctness compared to the true or accepted value.
Image Notes: All images are by A. Forgue, and may be copied, modified, and distributed freely.
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