Accuracy & precision Myers & Bryan -- RChem

Accuracy -- definition Accuracy refers to the closeness of measurements to the correct or accepted value of the quantity measured.

What is considered accurate? A teacher carefully measures the volume of alcohol in a 100 mL graduated cylinder with markings of 0.1 mL. The teacher’s reading (which, of course, is correct) is 76.84 mL. Several students then read the graduated cylinder. These are their measurements: Jake: 76.82 mL Lexie: 77.00 mL Tyler: 76.85 mL Isabelle: 76.78 mL Connor: 76.84 mL Whose measurements can be considered to be accurate? Why?

What is considered accurate? Metric ruler – 31 cm with 1mm (0.1cm) graduations. To which place should the length be estimated? ____________ This estimated digit is considered to be uncertain. How close to the accepted value do you think the measurement should be in order to be considered accurate? ______________ Why? Accepted measurement: 21.40 cm Which students are accurate? Student measurements: Erin: 21.50 cm Emily: 21.38 cm Ryan: 21.46 cm Manny: 21.41 cm Tr’evon: 30.40 cm

Precision -- definition Precision refers to the closeness of a set of measurements of the same quantity measured in the same way. (In other words, how close are a set of measurements to each other.)

Which data set is considered precise? TEAM BLUE TEAM ORANGE 42.68 g 42.56 g 43.68 g 42.58 g 42.86 g 42.57 g 39.88 g

When can measurements be both accurate and precise? The measurements must be close to each other as well as the accepted value. Next page:

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