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

2. Convert 2,780 ml in Liter 0.098 mg in µg 2.00 m in mm 0.04 L in ml

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

4. Evaluating Scientific Equipment

5. 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?

6. 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)

7. 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?

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

9. 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 ____ 9.6 +12.5+10.3+9.8=42.2 = 10.55g 4 10 g – 10.55 x 100% = 5.5% no negative % please!!! 10 g

10. 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

11. 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!

12. How to graph? Accuracy and Precision of Balance with 10 g weights g 10 5 A: 0.055 x 10.55 = +/-0.58 P: 0.275 x 10.55 = +/-2.90

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