what is the difference between precision and accuracy?

Answer 1

They almost have the same meaning.
But...
Accuracy means to be exact
Precision means to be brief and comprehensive and exact.

Accuracy may or may not be brief but precision is definitly brief.

Answer 2

ACCURACY:

The accuracy of an instrument indicates the deviation of the reading from a known input.
Accuracy maybe expressed in percentage, based on either actual scale reading or full scale reading, as follows:
percentage accuracy (based on actual scale) = (Vr-Va) / Va * 100
percentage accuracy (based on full scale) = (Vr-Va) / Vfs * 100

Vr ---> maximum or minimum result value
Va ---> actual value
Vfs --> full scale reading

For example: a 100 kPa pressure gauge having an accuracy of 1% would be accurate within + or - 1 kpa over the entire range of the gauge.


PRECISION:
The precision of an instrument indicates its ability to reproduce a certain reading with a given accuracy.
It is the degree of agreement between repeated results.
Precision refers to the repeatibility of measuring process, i.e., the closeness with which the measurement of the same physical quantity agree with one another.

As an example to differentiate between precision and accuracy, consider the measurement of a known voltage of 100 volts with a certain meter. Five readings are taken, and the indicated values are 104, 103, 105, 103 and 105 volts.

From these values, the accuracy of an instrument is

Accuracy = (Vr max. - Va) / Va * 100
= (105 - 100) / 100 * 100
= 5%
104+103+105+103+105 = 520 / 5
mean = 104

While precision is + or - 1% since the maximum deviation from the mean reading of 104 volts is only 1 volt.

It may be noted that, the instrument could be calibrated so that it could be used to dependably measure voltages within + or - 1 volt.

From this, it is clear that, accuracy can be improved up but not beyond the precision of the instrument by calibration.

Answer 3

Precision is the extent to which an experiment is reproducible and accuracy is the extent to which an experimental result agrees with a known or correct value. For ex. if you did an experiement 3 times and the results are constant than the experiment is very precise. Accuracy is when you know the result of the experiment. If it is really accurate then you get the same result each time. Accuracy deals with the result while precision deals with the actual experiment part.

Answer 4

precision is how close all of your measurements are to one another. You can have precision without accuracy. For example you take a measurement three times and get 8.56g, 8.52g, and 8.54g. The actual value should had been 9.12g. Although your precision was good, accuracy was not. Accuracy is then of course how close your measurements are to the actual value. So if you get 9.11g, 9.17g, and 9.14g your results would be both accurate and precise. Hope this helps

Answer 5

Accuracy refers to the ability to hit the target value. Think of a bullseye. Accuracy means that the shots to the target are in the center.

Precision refers to the ability to maintain little variation from a single value. Think again of a bullseye. Precision means that the grouping of all shots is very close to each other.

Consider that you can be precise (all shots grouped together) but not accurate (the grouping is far from the bullseye). Also consider that you can be accurate (the average number of shots hitting the bullseye is greater than missed), but not precise (the shots missing the bullseye are randomly scattered about the target fringes).

Accuracy of a measuring device means that it is capable of measuring a know value within a given degree of accuracy. Precision of the same device is the ability of the device to repeat a known measurement over and over. When listed on a specification these values are normally under idealized conditions (like a calibration lab). You should perform a gage R&R study to get accurate information in normal use.

Answer 6

Accuracy and Precision

To many people, accuracy and precision mean the same thing: to someone involved in measurement, the two terms should have very different meanings. In our learning of mathematics, we are taught to count, but not taught to measure. One way in which this distinction is apparent is the difference between a poll (a measurement) and a vote (a count). The result obtained from counting will be an exact result (barring blunder), while the result obtained from measuring will only approach the truth. We are taught how to deal with exact numbers, but are sometimes not aware of the nature of results we obtain from approximated or measured values.

Perhaps the easiest way to illustrate the difference between accuracy and precision is to use the analogy of a marksman, to whom the "truth" represents the bullseye.

Precision
the degree of refinement in the performance of an operation, or the degree of perfection in the instruments and methods used to obtain a result. An indication of the uniformity or reproducibility of a result. Precision relates to the quality of an operation by which a result is obtained, and is distinguished from accuracy, which relates to the quality of the result. A marksman may achieve uniformity but it may be inaccurate.

Accuracy
The degree of conformity with a standard (the "truth"). Accuracy relates to the quality of a result, and is distinguished from precision, which relates to the quality of the operation by which the result is obtained. A marksman may approach the "truth", although without great precision. It may be that he will need to change the equipment or methodology used to obtain the result if a greater degree of precision is required, as he has reached the limitations associated with his equipment and methodology.

Answer 7

The answer that used the example of the weather forecast is a good one. I teach engineering, and I use this example:

Up the road there is a little town that displays a sign reading, "Population 501." Does that mean that if a baby is born they shoot somebody? That is what the precise figure of "501" implies. "Precisely 501, no more and no less."

So the population report is precise, but not accurate. Experience tells us that there are likely to be more like 450 or 550 people bedding down in Littleton every night. If one counted the number of people who give Littleton as their residence address and the answer is 501, then an accurate figure might be stated, "Population 501, more or less."

The key is the variables. Weather is highly variable, and so are biological phenomena, including population.

If i count and say my neighbor's picket fence has 137 pickets, that is both accurate and precise. It is not subject to biological or other kinds of frequent variations.

Thus you will see that the difference between accuracy and precision is greater where there are many variables.

Answer 8

Precision refers to the degree of specified detail which can be observed; while accuracy refers to the truthfulness, or correctness, of the specified data.

Here's an example: The TV weather forecaster says that it will be between 40 and 60 degrees today. The actual reading turns out to be 53. Thus, the forecast was accurate, but not very precise. The forecaster provided a true statement but without enough detail for us to make plans. For tomorrow, the forecast is 52.47 degrees at 4 PM. It turns out to be 61 degrees. This forecast was very precise, but completely inaccurate.

Answer 9

Precision can have certain degrees, it means it can begin from totally wrong i.e. "black" to nearest correct, i.e. "white". There is a scope of grey area in between. While in accuracy, it is either accurate or inaccurate no scope for the grey area in between. Besides this precision can be used for measurements and accuracy can be used for mathematical calculations done after those measurements are taken.

Answer 10

Precision is used when a measure is right,but with slight differences(may be 98 or 99% right).
On the other hand accuracy to used to denote some measure which is 100% right.

Answer 11

Precision is the act of doing any job with the specified accuracy.