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Measurement Reliability

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

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  1. Measurement Reliability Precision & Accuracy

  2. 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.

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

  4. Precision & Accuracy

  5. Precision • Assesses data with many measurements and no accepted (target) value • Quantified using uncertainty • Largest deviation from mean • Smaller deviations, better precision

  6. Accuracy • Assess one measurement or many measurements • Quantified with % error • (experimental) – (accepted) X 100 (accepted)

  7. 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

  8. 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

  9. 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.

  10. Errors: Systematic Errors • Mistake which does not change during the experiment. • Affect accuracy, not precision.

  11. Measurement: Ruler

  12. Precision & Accuracy

  13. 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.

  14. 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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