## Accuracy vs Precision

Caroline Crotty 1D
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### Accuracy vs Precision

I remember the example we used in class, but I am unsure how to tell which is which. One is when all measurements are close together, but not the desired amount? The other is when all the measurements are on target?

Chem_Mod
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### Re: Accuracy vs Precision

Accuracy is on target. Precision is how closely you can repeatedly measure a thing.

Allen Chen 1J
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### Re: Accuracy vs Precision

Chem_Mod wrote:Accuracy is on target. Precision is how closely you can repeatedly measure a thing.

What is the chemistry context in which these differences will be most important?

Chem_Mod
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### Re: Accuracy vs Precision

It will be important when you do the experiment. Suppose you have a balance which you use to measure the mass of a chemical. The balance can have poor precision, meaning the numbers fluctuate all the time and you are not very certain. Or it can have good precision, where the numbers are always close if you measure the same thing over and over. I hope this example helps.

Bryan Jiang 1F
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### Re: Accuracy vs Precision

Caroline Crotty 1D wrote:I remember the example we used in class, but I am unsure how to tell which is which. One is when all measurements are close together, but not the desired amount? The other is when all the measurements are on target?

Accuracy means how close your measurements are to the true/correct value. Precision means how close your measurements are to each other. They are not mututally exclusive, so it is possible, as you said, that all measurements are close together but not the desired amount (very precise, but not very accurate). However, it is also possible that all measurements are close together and are the desired amount (both very precise and very accurate).
Last edited by Bryan Jiang 1F on Sun Apr 15, 2018 6:16 pm, edited 1 time in total.

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### Re: Accuracy vs Precision

Precision is how close to each other they are, and accuracy is how close to the true value they are.

Natalie_Martinez_1I
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### Re: Accuracy vs Precision

Accuracy tells you how close you are to the the true value, whereas precision indicates how close measurements are to one another.

Haison Nguyen 1I
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### Re: Accuracy vs Precision

Accuracy is how close your results are to the true value. Precision is how close your results are to each other.

Paywand Baghal
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### Re: Accuracy vs Precision

Allen Chen 1J wrote:
Chem_Mod wrote:Accuracy is on target. Precision is how closely you can repeatedly measure a thing.

What is the chemistry context in which these differences will be most important?

In context of chem, accuracy would be consistency getting the same, or around the same, answer when doing an experiment. Precision would be getting an answer which is correct.

KristinaNguyen_1A
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### Re: Accuracy vs Precision

I went to a UA office hour and how she described it was that:
Precision= how CLOSE measurements are to ONE ANOTHER
Accuracy= closeness of measurements to its TRUE VALUES

Maria Zamarripa 1L
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### Re: Accuracy vs Precision

Precision is how close the measurements are to one another and accuracy is how close the measurements are to the true value.

breannasung_1K
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### Re: Accuracy vs Precision

Precision is how close the measurements/ data are to one another. Accuracy is the closeness of the measurements/ data to their correct values.

When you have high precision and low accuracy, you can multiply all your data by some value to get higher accuracy.

004985802
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### Re: Accuracy vs Precision

accuracy measures how close your results are to the true value, and precision measures how exact and consistent your results are

Jessica Lancisi - 1I
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### Re: Accuracy vs Precision

@Paywand Baghal, I think that it would be the other way around- In a chemical context, accuracy would be getting the correct value, and precision would be getting the same or close to the same result each time. Precision without accuracy shows that there may be a mistake in the experiment that keeps getting repeated.

Rummel Requerme 1E
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### Re: Accuracy vs Precision

Essentially accuracy is how close you are to the actual result, as precision is how close your results are in respect to one another.

Hope_Pham_1G
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### Re: Accuracy vs Precision

When visualizing accuracy, think of a bulls-eye target with many shots near the center, but scattered within the radius of the bulls-eye in any direction. The results appear very disbursed. When visualizing precision, think of a bulls-eye target with many shots clumped together, but not necessarily within close range of the bulls eye. The important aspect of precision is that the same value is achieved consistently even if the value is not equal to the true value.

Taizha 1C
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### Re: Accuracy vs Precision

According to lecture precision indicates how close measurements are to one another while accuracy is the accuracy to the true value.

Eugene Chung 3F
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### Re: Accuracy vs Precision

ran2000
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### Re: Accuracy vs Precision

From an experimental chemistry standpoint, an example of accuracy vs. precision would be:
If we conducted an experiment to test the volumes of carbon dioxide released when different concentrations of acid were added to metal carbonates, the study would have-
1. Low accuracy and Low precision if the the volumes of CO2 were found to be very variable (1.3l, 1.7l, 1.8l, 1.0l, 1.6l) and the method used to measure it was wrong (such as the calculating the volume of a balloon after it filled up with CO2, but without maintaining a constant temperature)
2. Low accuracy but high precision if the volumes of CO2 were found to be very close to one another (1.0l, 1.1l, 1,0l, 1.1l, 1.0l) but the method used had a systematic error such as the method of measurement of volume would not provide the actual volume measurement.
3. High accuracy but low precision if the volumes of CO2 were found to be variable (1.7l, 1.9l, 1.1l, 1.4l, 2.0l) but the method of volume measurement did not have any systematic errors, rather the variability in the volume was a problem of random errors.
4. High accuracy and high precision if the volumes of CO2 were found to be close to each other (1.0l, 1.1l, 1.0l, 1.0l, 1.1l) and the method of volume measurement did not have any systematic errors (the method used to measure volume would provide the true values)

ariellasarkissian_3H
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### Re: Accuracy vs Precision

Caroline Crotty 1D wrote:I remember the example we used in class, but I am unsure how to tell which is which. One is when all measurements are close together, but not the desired amount? The other is when all the measurements are on target?

Accuracy is how close your value is to the true/exact value. Precision is producing values that are close in proximity. In some cases, if you receive the same value multiple times you are precise, but if it is not close to the exact value, you are not accurate.

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Joined: Fri Sep 28, 2018 12:23 am

### Re: Accuracy vs Precision

So there are four scenarios
1. Low accuracy and low precision
2. Low accuracy and high precision
3. High accuracy and low precision
4. High accuracy and high precision
Obviously we are shooting to get high accuracy and high precision; although, in the event that your data isn't, would it be worse to have high accuracy and low precision or low accuracy and high precision?

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### Re: Accuracy vs Precision

Another interesting definition of accuracy - Accuracy can be defined as when the average experimental value is close to the true value. For example, if the three following measurements were taken of a 30 mL sample of water: 20 mL, 35 mL, and 35 mL, the average value of this measurement is 30 mL. By this definition, the sample is considered accurate but not precise.

Rebecca Altshuler 1D
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### Re: Accuracy vs Precision

How can values be accurate but not precise? If all the values are accurate (close to the true value) how can they still be not precise in relation to each other?

Elena Maneffa 1E
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### Re: Accuracy vs Precision

Rebecca Altshuler 1E wrote:How can values be accurate but not precise? If all the values are accurate (close to the true value) how can they still be not precise in relation to each other

Values can be accurate but not precise because each measurement may be close to the true value (relatively) however not relatively close enough to each other to be considered precise.

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