Expert: Bobby Soltani - 9/19/2004

Question
How can you figure out what is good precision and accuracy? I asked my teacher and he explained to me how to do the percent error. What I forgot to ask him was how do you know from the percent of error if something is accurate or precise or both. I have a test coming up in 2 days and won't see him till then so if you could help me, it would be a great help. Have a good day.

Answer
Hi Jeff,

I'll take a shot at the answer.

If you take 5 shots at a bullseye and all 5 shots fall within a few inches of the bullseye, you are accurate, but not exactly precise.

If you take 5 shots at a bullseye and miss everytime exacly 2 feet to the right of the bullseye, you are precise but not accurate.

These terms are qualitative in that there is no exact cutoff between what is precise, accurate or both.


Note: after reading my explanation, I saw that it can still be very confusing.  In attempt to find a better example, I stumbled upon a website that has a good explanation.  Check it out and let me know if you have further questions.

Bobby

http://www.wcsscience.com/precision/andaccuracy.html