Presentation on theme: "Accuracy and Precision"— Presentation transcript:
1 Accuracy and Precision Measurements are qualitative or quantitative.Qualitative measurements give results that are descriptive and non-numerical.Example:Quantitative measurements give results that are definite, usually as numbers and units.
2 Accuracy and Precision Measurements work best when they are accurate and preciseAccuracy is a measure of how close a measurement comes to the actual or true value of whatever is measured.To evaluate the accuracy of a measurement, it must be compared to the correct value.Precision is a measure of how close a series of measurements are to one another.The precision of a measurement depends on more than one measurement.
5 Accuracy and Precision In this picture, all of the darts land on the bulls-eye which illustrates good precision and accuracy.In this picture, all of the darts land near each other, but away from the bulls-eye which illustrates good precision, but poor accuracy.
6 Accuracy and Precision Here the darts are not close to each other, but are close to the bulls-eye indicating poor precision, but good accuracy.Finally, the darts are not close to each other or near the bulls-eye indicating both poor accuracy and poor precision.
7 Accuracy and Precision Sometimes there is a difference between the accepted value and the experimental value.This difference is known as error.Error = accepted value – experimental valueError can be positive or negative depending on whether the experimental value is greater than or less than the accepted value.
8 Accuracy and Precision Often it is useful to calculate relative error, or percent error.Percent error = error x 100%accepted valueThe percent error will always be a positive value.