Reliability of a Measurement: Precision versus Accuracy and Uncertainty

• Precision

• Agreement/closeness of repeatable values
• Note: You can be precise but not accurate in measurements.

• Accuracy

• Agreement/closeness of measured values to actual known value
• Note: You can have accuracy in overall measurement but not be precise.

• Uncertainty or Confidence factor

• Degree of measurement/value differs
• Reported as (+/–) and usually determined using statistical methods
• Example
• 23.45 +/– 0.05 indicates the level of confidence (0.05) in a reported value.
• The value obtained lies within 23.40 to 23.50.