Percent Error

Percentage error is a measurement of the discrepancy between an observed (measured) and a true (expected, accepted, known) value. It is typically used to compare measured vs. known values as well as to assess whether the measurements taken are valid. When measuring data, the measured value often varies from the true value. Error can arise due to many different reasons that are often related to human error, but can also be due to estimations and limitations of devices used in measurement. Calculating the percentage error provides a means to quantify the degree by which a measured value varies relative to the true value.

The computation of percentage error involves the use of the absolute error, which is simply the difference between the observed and the true value. The absolute error is then divided by the true value, resulting in the relative error, which is multiplied by 100 to obtain the percentage error.

Negative percentage error: When the true value is positive, percentage error is always positive due to the absolute value. However, it is possible to have a negative percentage error if we do not take the absolute value of the error. A negative percentage error simply means that the observed value is smaller than the true value.