Accuracy and precision are two important concepts in science. Both terms apply to any experimental measurement you make. But what do they actually mean? What is the difference between them and which is more important?
Accuracy is a measure of how close your experimental measurements agree with known values. The closer your measurements are to the known value, the more accurate the measurement.
If you think of the known value as the bullseye on a target, accurate shots (or measurements) would be where the average of your shots would be at or near the bullseye. The shots in this picture are accurate, but they are all over the target. This brings up the concept of precision.
Precision is a measure of how close your experimental measurements agree with each other. The closer each measurement is to the other measurements, the more precise your measurement.
If the measurements were shots in a target, the closer the holes are to each other, the more precise the shots. Here, the shots are all clustered together. They would be considered a precise collection of shots. The only problem is they are not very accurate.
How can I control accuracy and precision?
Both accuracy and precision should be the goal of any measurement. Variations in accuracy and precision are generally within your own control. In target shooting, you could improve accuracy by moving closer to the target, or using an aiming aid like a scope or laser pointer. You can improve precision by mounting your gun to a table or bench or shooting indoors out of the wind. In general, use good tools designed for the measurement you are trying to make and pay close attention to what you are doing when you use them. This will help any measurement you try to make.
Which is more important, precision or accuracy?
Accuracy is generally more important when trying to hit a target. You either hit your target or you don’t. It does no good to be precise if you miss all your shots. Although, you can improve accuracy in future measurements by factoring in a correction factor. If your shots are all going to the left, alter your aim to the right. Accuracy is something you can fix in future measurements.
Precision is more important in calculations. When using a measured value in a calculation, you can only be as precise as your least precise measurement. This is the main idea behind the topic of significant figures in calculations. Precision can be improved by improving your measuring tool and/or improving your skill at using the tool.
Accuracy and precision are both important to good measurements in science. Try to make the best of both in all your measurements.