Measurement Reliability

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.

12. Measurement: Ruler

13. Precision & Accuracy

14. 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.

15. 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.