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Accuracy, precision and % error

Accuracy, precision and % error. Uncertainty in Measurements. There is ALWAYS uncertainty in a measurement. Instruments are not perfect Measuring involves some estimation. Uncertainty in Measurements. So how do we know if our measurements are good?! We check their…

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Accuracy, precision and % error

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  1. Accuracy, precision and % error

  2. Uncertainty in Measurements • There is ALWAYS uncertainty in a measurement. • Instruments are not perfect • Measuring involves some estimation

  3. Uncertainty in Measurements • So how do we know if our measurements are good?! We check their… ACCURACY And PRECISION

  4. Precision = Repeatability How well do the experimental values agree with each other? • Repeat a measurement several times, conduct trials! • If your values are PRECISE, they are very close to each other , whether or not they are correct (accurate). • If your values are NOT PRECISE, they are not very close to each other, whether or not they are correct (accurate)

  5. Accuracy = close to “accepted value” Compare… • If a value is ACCURATE it is CORRECT. (You’re right!!) • If a value is NOT ACCURATEit is INCORRECT. (You’re wrong….) The information or answer that you should have gotten performing the experiment. The information or value you get from performing your experiment. to

  6. How good is your measurement? Precision = Repeatability Accuracy = close to “accepted value” What can you conclude about accuracy and precision from the image? Precise; inaccurate

  7. How good is your measurement? What can you conclude about accuracy and precision from the image? Inaccurate; low precision

  8. How good is your measurement? What can you conclude about accuracy and precision from the image? Precise; accurate

  9. How good is your measurement? Example: Suppose a hermit crab habitat is supposed to be kept at 75.0 F. A warmer with a thermostat is placed into the terrarium and temperature readings are taken 5 times giving the data shown to the right. What can you conclude about the accuracy and precision of the warmer? Accuracy _________ Precision ____________ Temp Readings 77.3 F 77.2 F 76.9 F 77.0 F 77.2 F

  10. How accurate is my measurement? • The accepted value is the true or correct value (what you SHOULD have gotten). • The measured value is what YOU measured or calculated yourself. • Notice that the numerator is in absolute value form. You should not have any negative percent error values.

  11. Example • A student buys a rope at the store. The label on the packaging says that the rope is 2.15 meters in length. The student measures the rope as 1.85m. What is the student’s percent error? Accepted = 2.15 m Measured – 1.85 m % error = = 14.0%

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