Accuracy vs. Precision


Accuracy and precision are used in context of measurement. Accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value, while precision is the degree to which further measurements or calculations show the same or similar results. In other words, the precision of an experiment/object/value is a measure of the reliability of the experiment, or how reproducible the experiment is. The accuracy of an experiment/object/value is a measure of how closely the experimental results agree with a true or accepted value.

Both accuracy and precision are terms used in the fields of science, engineering and statistics.

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Definition The degree of closeness to true value. The degree to which an instrument or process will repeat the same value.
Measurements Single factor or measurement Multiple measurements or factors are needed
About A term used in measuring a process or device. A term used in measuring a process or device.
Uses Physics, chemistry, engineering, statistics and so on. Physics, chemistry, engineering, statistics and so on.

Contents: Accuracy vs Precision

edit Example

One can say that a measurement is accurate but not precise; precise but not accurate; neither or both. An example of bad precision and good accuracy can be: Suppose a lab refrigerator holds a constant temperature of 38.0 F. A temperature sensor is tested 10 times in the refrigerator. The temperatures from the test yield the temperatures of: 37.8, 38.3, 38.1, 38.0, 37.6, 38.2, 38.0, 38.0, 37.4, 38.3. This distribution shows no impressive tendency toward a particular value (lack of precision) but each value does come close to the actual temperature (high accuracy).

edit Target comparison

Accuracy is the degree of veracity while precision is the degree of reproducibility. Target comparison can be used to explain this difference between the two terms. If arrows are fired at a target and measurements are taken then accuracy will describe the closeness of the arrows to the bullseye at the target center. Arrows that strike closer to the bullseye are considered more accurate. The closer a system's measurements to the accepted value, the more accurate the system is considered to be. If a large number of arrows are fired, precision would be the size of the arrow cluster. (When only one arrow is fired, precision is the size of the cluster one would expect if this were repeated many times under the same conditions.) When all arrows are grouped tightly together, the cluster is considered precise since they all struck close to the same spot, if not necessarily near the bullseye. The measurements are precise, though not necessarily accurate. However, it is not possible to reliably achieve accuracy in individual measurements without precision.

edit Number of measurements

Another difference between the two can be that accuracy can be determined by one measurement while many measurements are needed to determine precision. In the above example, by just one arrow fired, one knows if it is accurate or no but a number of arrows have to be fired to know if the result is precise or no.

edit Quality

While a precise measurement may speak highly of an instruments quality, an accurate reading will not reflect on the quality. Accuracy is an agreement of a measured value with an expected value. Another example: A stopped clock will be accurate twice in day, but it will not be precise - a reflection on its quality. If a clock reflects the right time in 10 readings at 10 different points in time it can be considered precise and therefore of high quality.

edit Applications

Both Accuracy and Precision can be used in quantifying and statistics, physics, engineering and logic testing.

edit References

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Comments: Accuracy vs Precision

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Anonymous comments (10)

May 16, 2014, 3:42pm

good definition

— 107.✗.✗.27

May 3, 2014, 9:33am


— 223.✗.✗.245

April 6, 2014, 7:21am

advantage of hay bidge

— 91.✗.✗.117

March 23, 2014, 4:59am

now i understand

— 37.✗.✗.8

December 23, 2013, 9:55pm


— 141.✗.✗.115

October 30, 2013, 4:36pm

i am still confused about it???????????????????????????????

— 39.✗.✗.227

October 7, 2013, 1:22pm

how can somthing be prisise and accuraty i do not understand

— 8.✗.✗.70

August 1, 2013, 7:51pm

thnxxxx alot

— 115.✗.✗.34

July 11, 2012, 3:33pm

Accuracy can be improved by taking repeat measurements and taking an average. (This assumes that errors are randomly above and below the true value to the same degree) Therefore an experiment with a low degree of precision can provide accurate values where appropriate statics are applied.
Conversely, precision cannot be improved by taking repeat results but it is impossible to quantify precision without experimental repeats.
The danger when evaluating an experiment is that some errors are not random. In this case an experiment could yield inaccurate results yet be highly precise.
Mathematically: accuracy is the closeness to the true answer where as precision is the standard deviation from the average result.

— 193.✗.✗.1

April 20, 2012, 8:49am

Something said to be accurate can also be precise, now on the other hand something precise don't have to be accurate weird right. Think about it.

— 208.✗.✗.244


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