Accuracy & precision

Overview

  • Focus areas:

    • Importance of accuracy and precision

    • Definitions of accuracy and precision

    • Issues surrounding measurement errors

Importance of Accuracy and Precision

  • All instruments possess some level of uncertainty in measurements.

  • Different types of measurement errors exist; understanding these is crucial.

  • A structured framework is required to address measurement uncertainties effectively.

High Quality Meteorological Instrument

  • Campbell Scientific EE181-L:

    • Air Temperature and Relative Humidity Sensor.

    • Features:

      • Rugged and ideal for long-term applications.

      • Proprietary coating enhances the reliability of the RH element.

      • Temperature range: -40° to +60°C, with an accuracy of ±0.2°C at +23°C.

      • Needs recalibration annually for optimal results.

      • Compatible with most Campbell Scientific dataloggers.

Measurement Uncertainty

  • Measurement involves some uncertainty or error, and the "true value" cannot be precisely known.

  • Close examination of errors is critical for improving measurements.

  • Consideration of instrument errors and types of measurement errors is important for effective measurement practices.

Definitions of Accuracy and Precision

Accuracy

  • Definition: Closeness of measurements to the true value.

    • Measurements are considered accurate if their average aligns closely with the true value.

    • Expressed in absolute or relative values.

    • Example: Accuracy of temperature readings can be influenced by various factors.

Precision

  • Definition: Closeness of repeated measurements to one another.

    • Measurements are precise if repeated values exhibit minimal variability.

    • Can be quantified using standard deviation and repeatability.

Relationship Between Accuracy and Precision

  • Accuracy and precision are independent of each other.

    • Measurements can be accurate, precise, both, or neither.

Dealing with Measurement Errors

  • Expect random variability and measurement errors.

    • Accuracy relates to systematic bias; precision relates to random variability.

  • Low accuracy poses significant challenges, making it difficult to ascertain how far measurements are from the true value.

  • Low precision can still facilitate quantifiable improvements through statistical methods.

Reporting Measurement Errors

  • Report errors explicitly with positive and negative margins (e.g., ±0.2°C).

  • Utilize significant figures to imply limits of accuracy implicitly.

    • Example: 7.54398(23) × 10−10 m indicates a precision range.

Summary

  • Accuracy involves systematic error; precision involves random error.

  • Independent nature of accuracy and precision impacts measurement validity.

  • Enhancing precision is possible through consistent methodology, while improving accuracy requires improved methods.

  • Always report expected errors comprehensively to maintain the integrity of measurements.