accuracy vs. precision?

[jonnylane]

I was told that this could be a question in an interview for a job i applied for: What is the difference between accuracy and precision?

I pondered it for a long time, and today i found this:

http://www.flatsurv.com/accuprec.htm

Try leaving a reply as your answer and then check it out!

Weird...

[GuchiGuh]

my english is not the greatest, but i think precision is the degree to what something is done and to what level of detail, and accuracy is to what degree of precision something has been done.... not sure, but I hope it helps!
btw that article....waaahhh whay too hard english....bugger

[Jammrock]

http://www.m-w.com/
Main Entry: ac·cu·ra·cy
Pronunciation: 'a-ky&-r&-sE, 'a-k(&-)r&-
Function: noun
Inflected Form(s): plural -cies
Date: 1662
1 : freedom from mistake or error : CORRECTNESS
2 a : conformity to truth or to a standard or model : EXACTNESS b : degree of conformity of a measure to a standard or a true value -- compare PRECISION 2a

http://www.m-w.com/
Main Entry: 1pre·ci·sion
Pronunciation: pri-'si-zh&n
Function: noun
Date: 1740
2 a : the degree of refinement with which an operation is performed or a measurement stated -- compare ACCURACY 2b b : the accuracy (as in binary or decimal places) with which a number can be represented usually expressed in terms of the number of computer words available for representation (double precision arithmetic permits the representation of an expression by two computer words)

In my own words, accuracy is the ability to 'hit a mark.' An accurate sharpshooter can hit a bullseye.

Precision is the ability to consistently be accurate. A precise sharpshooter can hit the same spot, within 3 cm, over and over again.

I suppose the example changes from subject to subject.

My $0.02.

Jammrock

[cjolley]

I have measured the distance to the moon to a precision of .00001 meters:
1234.56789 M

Unfortunately, my measurement does not appear to be accurate.
chuck

PS It's just how finely divided a ruler you use -vs- how close you get to the real value.

[Marshmallowman]

Jammrock, thats apretty accurate description. Almost as I remember it from doing physics at uni .

eg accurate: a spray all within ceratin range of the target.

precision : may all be well off target but are consistantly in the same area...eg good marksman shooting with an unsighted scope.

so you can be very precise but inaccurate

[jonnylane]

you learnt it in uni?

how come i haven't been taught it?

I feel cheated!

[WyWyWyWy]

Accuracy is telling the truth . . . Precision is telling the same story over and over again.
Yiding Wang, yiwang@mtu.edu

Very well said.

[agallag]

I was taught the difference in grade 12 physics. I had a great teacher that year...

[Brian Ellis]

The article you quote is excellent.

Remember that the precision of, say, a voltmeter may be described as +/- 1% FSD (full scale deflection) for an analogue instrument or +/- 0.2% +/- 1 LSD (lowest significant digit) for a digital instrument. This means that, if you read 0.5 V on the analogue instrument set to a range of 1 V, the real value may be anything 0.49 to 0.51 (+/-1% of 1 V). If the digital instrument reads 0.500 V, on a range reading up to 1.999 V, it could be from 0.495 to 0.505 (+/- 0.2% of 1.999 +/-0.001). However, the accuracy of your measurement may be affected by the internal resistance of your instrument. If the voltage you are measuring has a source resistance of, say, 1 kilohm and your analogue voltmeter has an internal resistance of 9 kilohms (usually higher in practice, but easy figure for illustration), then 1/10 of your source voltage is dropped across the source impedance, and 9/10 across your voltmeter, which will then read about 0.45 V, instead of 0.5 V. If you use your digital voltmeter, with an internal resistance of 10 megohms, then the accuracy will be practically unaffected and will read 0,5 V within the precision of the instrument.

Another semantic confusion of a similar nature is 'about' and 'approximately'. If you say something costs about a dollar, it may be, say, anything from 95 c to $1.05, according to your scale of precision, including $1.00. If it is approximately one dollar, it may be between 95 c and $1.05, but never exactly $1.00. Subtle! It comes from the Latin proximus, meaning very near.

[Helevitia]

Something I learned in construction...

When building a house, as long as we were within an 1/8" we would considered accurate Was it precise? no.

Dave

[MultimediaMan]

Jammrock's definition and example is the most concise metaphors for conveying the difference between precision and accuracy.

Wywywywy's example is much more politically correct.

[GuchiGuh]

this is getting really confuzing...

[cjolley]

Originally posted by Helevitia
Something I learned in construction...

When building a house, as long as we were within an 1/8" we would considered accurate Was it precise? no.

Dave

Certainly it was precise.
With ±(½)³ in. precision.
Certainly precise enough for a house.

But it realy wasn't very accurate.

Chuck

[WyWyWyWy]

Originally posted by MultimediaMan
Jammrock's definition and example is the most concise metaphors for conveying the difference between precision and accuracy.

Wywywywy's example is much more politically correct.

Mine is more accurate and his is more precise

[Sethos]

Accuracy is being able to add 1 and 1 and get 2.

precision is doing so when drunk

~Sethos

PS. the drunk answer tends to be 11