Precision Vs Accuracy
In Quality Management, there is a "pair" of terms, Precision & Accuracy. It may feel similar, that is what I have always been thinking. But, they are different. Following are what they mean as per PMBOK
Precision: Measurements falling close to each other
Accuracy: Degree of conformity of measurements to the true value
Now, this may seem confusing. But, it is pretty easy. I'll explain with an example. In our college first year, we used to a physics experiment... three hours of physics lab in a sleepy afternoon :(
The experiment is conducted to find out the value of "g", earth's gravity, which everyone knows as 9.81m/s2 (Whatever that means). We used to find that out all over again by rotating some wheel kind of appratus tied to a rope and some weight (ball?). I do not remember it exactly now, but it was something like replacing weights and rotating the wheel and take some measurements followed by some calculations... And there I got the "g" value .... 7.3. May be my experiment was conducted somewhere in the space in between the earth and moon. Okay, now I realized the rotation of the wheel was too slow and did it all over again to get the value.. 15.2 Oops..!!!
There were four people doing the same experiment in the lab at that time: Kesara, Nabil, Shamim and Hari (All names fictitious until the name owenrs see this article). Following were their measurements in five attempts.
Nabil : 8.2, 8.1, 7.9, 8.4, 8.1 - This is Precise but not Accurate
Shamim : 10.7, 9.4, 10.6, 10.2, 9.6 - This is Less Precise than Nabil's measurements, but More Accurate
Kesara : 9.7, 9.8, 9.9, 9.8, 9.6 - This is More Precise then previous two and More Accurate as well. Kesara is always like that :)
And Finally we have...
Hari: 7.3, 15.2, 6.4, 13.5, 4.8 - Nether Precise Nor Accurate. Hari is always like that :)
Hope the example is easy to understand and remember. If you find anything incorrect or appropriate in this, please feel free to leave a comment.
Precision: Measurements falling close to each other
Accuracy: Degree of conformity of measurements to the true value
Now, this may seem confusing. But, it is pretty easy. I'll explain with an example. In our college first year, we used to a physics experiment... three hours of physics lab in a sleepy afternoon :(
The experiment is conducted to find out the value of "g", earth's gravity, which everyone knows as 9.81m/s2 (Whatever that means). We used to find that out all over again by rotating some wheel kind of appratus tied to a rope and some weight (ball?). I do not remember it exactly now, but it was something like replacing weights and rotating the wheel and take some measurements followed by some calculations... And there I got the "g" value .... 7.3. May be my experiment was conducted somewhere in the space in between the earth and moon. Okay, now I realized the rotation of the wheel was too slow and did it all over again to get the value.. 15.2 Oops..!!!
There were four people doing the same experiment in the lab at that time: Kesara, Nabil, Shamim and Hari (All names fictitious until the name owenrs see this article). Following were their measurements in five attempts.
Nabil : 8.2, 8.1, 7.9, 8.4, 8.1 - This is Precise but not Accurate
Shamim : 10.7, 9.4, 10.6, 10.2, 9.6 - This is Less Precise than Nabil's measurements, but More Accurate
Kesara : 9.7, 9.8, 9.9, 9.8, 9.6 - This is More Precise then previous two and More Accurate as well. Kesara is always like that :)
And Finally we have...
Hari: 7.3, 15.2, 6.4, 13.5, 4.8 - Nether Precise Nor Accurate. Hari is always like that :)
Hope the example is easy to understand and remember. If you find anything incorrect or appropriate in this, please feel free to leave a comment.
