Measurement reliability
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Measurement Reliability. Precision & Accuracy. Precision. The degree to which several measurements provide answers very close to each other. Indicator of the scatter in the data. The less the scatter, The higher the precision. . Accuracy.

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Measurement reliability

Measurement Reliability

Precision & Accuracy


Precision
Precision

  • The degree to which several measurements provide answers very close to each other.

  • Indicator of the scatter in the data.

    • The less the scatter, The higher the precision.


Accuracy
Accuracy

  • The nearness of a measurement to the standard or actual value.



Precision1
Precision

  • Assesses data with many measurements and no accepted (target) value

  • Quantified using uncertainty

    • Largest deviation from mean

    • Smaller deviations, better precision


Accuracy1
Accuracy

  • Assess one measurement or many measurements

  • Quantified with % error

    • (experimental) – (accepted) X 100 (accepted)


Accurate or precise
Accurate or Precise?

  • Baseball player hits the ball directly to the shortstop every time at bat.

  • Darts player hits the bulls eye with every shot.

Precise

Precise & Accurate


Accurate or precise1
Accurate or Precise?

  • Soccer player hits the right goal post with every shot on goal.

  • Basketball player sometimes makes a basket, sometimes bounces off the rim, sometimes hits the back board, and sometimes shoots straight over the back board.

Precise

Not Precise Or Accurate


Errors random errors
Errors: Random Errors

  • Unnoticed variations in technique, tiny changes in the experimental environment, etc.

  • Affect precision.

  • Truly random effects average out over a large number of trials.


Errors systematic errors
Errors: Systematic Errors

  • Mistake which does not change during the experiment.

  • Affect accuracy, not precision.




Uncertainty calculations
Uncertainty Calculations

  • Calculate mean

  • Calculate difference between each measurement and the mean (the deviation)

  • Use the largest of these values as the uncertainty

  • The smaller the range, the more precise.


Uncertainty calculations1
Uncertainty Calculations

  • Calculate mean

  • Calculate difference between each measurement and the mean (the deviation)

  • Use the largest of these values as the uncertainty

  • Value in range of 0.741 to 0.765

  • The smaller the range, the more precise.


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