Answer to Question #135612 in Physics for sara

Question

Describe accuracy and precision and how they relate to to data and how mean and standard deviation tell us about time measurement data.

Answer 1

The normalised standard deviation is known as the coefficient of variation (CV).

Precision refers to how closely individual measurements agree to each other, the lower the CV, the more precise the values. 

Accuracy refers to the degree of conformity of a measured or calculated quantity to an actual (true) value. Accuracy is closely related to precision, but it’s not the same thing. A result is said to be accurate when it matches to a particular target. Let’s look at a common analogy to illustrate the difference between accuracy and precision.

1. High accuracy with high precision.

 When results have both a high degree of accuracy and precision they will be clustered together around the target area (true value).  In this example there is no bias.

2. Low accuracy with high precision.

Results that are precise will be clustered together, but because they are inaccurate they will not be near the target area (true value). This is an example of bias, the measured value deviates from the target value.

3. Low accuracy with low precision.

Results with both low precision and low accuracy will be scattered about, and may not be near each other or the target area. Due to the poor quality of results we can’t say if there is bias present in this case.

Standard deviation tells you how spread out the data is. It is a measure of how far each observed value is from the mean. In any distribution, about 95% of values will be within 2 standard deviations of the mean.