Indicate the length up to one estimated value…. A. B. C.

Convert 2,780 ml in Liter mg in µg 2.00 m in mm 0.04 L in ml

Measure the volumes on stations 1-8 You need at least 1 measured and at least 1 estimated value in your measurements

Evaluating Scientific Equipment

Measurement are evaluated based on the following parameters 1. Accuracy: How close are measurements to an ‘ideal/true value’? 2. Precision: How close are measurements to each other?

Other Statistical Key Terms True Value: An ideal/perfect measurement, a reference value Note: does often not exist in exploratory research! Average/Mean: Arithmetic Mean: sum of all measurements divided by number of measurements (n)

Target Practice Analogy What’s the true value in pictures A-C? Identifiy which one you think is accurate/precise A B C NOTE: A good measurement should be highly accurate and highly precise!!! Which one is it?

Formulas: Accuracy (% Error) A = true value – average value x 100% true value Precision (% Range) P = highest value – lowest value x 100% average value

Example: A lab tech has to calibrate a balance with 10.0 g weight samples. He makes 4 repeat measurements: 9.6 g, 12.5g, 10.3 g and 9.8 g. Calculate accuracy and precision of the balance….. Accuracy: (% Error) true value – average value x 100% true value Find the following: True Value ____ 10.0g Average Value ____ =42.2 = 10.55g 4 10 g – x 100% = 5.5% no negative % please!!! 10 g

Precision (% Range) highest value – lowest value x 100% average value Find Highest value ___ Lowest value ____ Average value ____ 12.5 g – 9.6 g x 100% = 27.5% 10.55g

Accuracy: 5.5% Precision 27.5% Note: the larger the %, the worst the quality! Result statement: Balance is more accurate than precise!!! Think: Why accuracy alone is not a good indicator? Values can average out to be close to the true value (high accuracy), but precision will reveal it!

How to graph? Accuracy and Precision of Balance with 10 g weights g 10 5 A: x = +/-0.58 P: x = +/-2.90

Statistical tool used w/o true values Variance: Average of squared differences from the mean Standard Deviation: Square root of the Variance