Accuracy
-Accuracy is how close you are to the true value. For example, let’s say you know your true
height is exactly 5’9″.
-correctness of the value in correlation with the information
You measure yourself with a yardstick and get 5’0″. Your measurement is not accurate.
You measure yourself again with a laser yardstick and get 5’9″. Your measurement is
accurate.
Note: The true value is sometimes called the theoretical value.
Precision
-Precision is how close two or more measurements are to each other. If you consistently
measure your height as 5’0″ with a yardstick, your measurements are precise.
-is a measure of how much detailed information is given
3.14-accurate but not precise because less significant digits are given
3.14169…-precise but not accurate because more significant digits of information is given
Accuracy of Analysis and Precision Together
If you are precise, that doesn’t necessarily mean you are accurate. However, if you are
consistently accurate, you are also precise.
“More” Precise
If you want to tell which set of data is more precise, find the range (the difference between
the highest and lowest scores). For example, let’s say you had the following two sets of data:
Sample A: 20, 15, 11, 9, 8, 14
Sample B: 19, 13, 14, 11, 12, 9
Subtract the lowest data point from the highest:
The lower the range, the more precise.
More Examples
Accurate and precise: If a weather thermometer reads 75oF outside and it really is 75oF, the
thermometer is accurate. If the thermometer consistently registers the exact temperature for
several days in a row, the thermometer is also precise.
Precise, but not accurate: A refrigerator thermometer is read ten times and registers degrees
Celsius as: 39.1, 39.4, 39.1, 39.2, 39.1, 39.2, 39.1, 39.1, 39.4, and 39.1. However, the real
temperature inside the refrigerator is 37 degrees C. The thermometer isn’t accurate (it’s almost
two degrees off the true value), but as the numbers are all close to 39.2, it is precise.