Accuracy and Precision

Accuracy

Accuracy is how close a measured value is to the actual (true) value.

Precision

Precision is how close the measured values are to each other.

Bias (don't let precision fool you!)

When we measure something several times and all values are close, they may all be wrong if there is a "Bias"

Bias is a systematic (built-in) error which makes all measurements wrong by a certain amount.

Examples of Bias

• The scales read "1 kg" when there is nothing on them
• You always measure your height wearing shoes with thick soles.
• A stopwatch that takes half a second to stop when clicked

In each case all measurements are wrong by the same amount. That is bias.

Reference

http://www.antarcticglaciers.org/glacial-geology/dating-glacial-sediments-2/precision-and-accuracy-glacial-geology/

http://www.mathsisfun.com/accuracy-precision.html