Trueness

Trueness is the closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value.

Trueness is not a quantity and therefore cannot be expressed numerically. Rather it is expressed as bias.

• Bias
  Bias is a measure of a systematic measurement error, the component of measurement error that remains constant in replicate measurements.
• Linearity
  Nonlinear bias is a component of bias that cannot be represented by a linear relationship between the measured and true values.
• Interferences
  Interference bias is a component of bias caused by nonspecificity attributable to the presence of a specific interfering substance.