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Accuracy and Precision Accuracy and Precision Ck12 Science Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) AUTHOR Ck12 Science To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2013 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Com- mons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: September 15, 2013 www.ck12.org Concept 1. Accuracy and Precision CONCEPT 1 Accuracy and Precision • Define accuracy. • Define precision. • Describe situations with varying levels of accuracy and precision. How do professional basketball players improve their shooting accuracy? Basketball is one of those sports where you need to hit the target. A football field goal kicker might have room for some deviation from a straight line – for college and pro football there is an 18 foot 6 inch space for the ball to go through. In basketball, the basket is only 18 inches across and the ball is a little less than 10 inches across – not much room for error. The ball has to be on target in order to go into the basket and score. Accuracy and Precision In everyday speech, the terms accuracy and precision are frequently used interchangeably. However, their scientific meanings are quite different. Accuracy is a measure of how close a measurement is to the correct or accepted value of the quantity being measured. Precision is a measure of how close a series of measurements are to one another. Precise measurements are highly reproducible, even if the measurements are not near the correct value. Darts thrown at a dartboard are helpful in illustrating accuracy and precision Assume that three darts are thrown at the dartboard, with the bulls-eye representing the true, or accepted, value of what is being measured. A dart that hits the bulls-eye is highly accurate, whereas a dart that lands far away from the bulls-eye displays poor accuracy. The Figure 1.1 demonstrates four possible outcomes. a. The darts have landed far from each other and far from the bulls-eye. This grouping demonstrates measure- ments that are neither accurate, nor precise. 1 www.ck12.org FIGURE 1.1 The distribution of darts on a dartboard shows the difference between accuracy and precision. b. The darts are close to one another, but far from the bulls-eye. This grouping demonstrates measurements that are precise, but not accurate. In a laboratory situation, high precision with low accuracy often results from a systematic error. Either the measurer makes the same mistake repeatedly or the measuring tool is somehow flawed. A poorly calibrated balance may give the same mass reading every time, but it will be far from the true mass of the object. c. The darts are not grouped very near to each other, but are generally centered around the bulls-eye. This demonstrates poor precision, but fairly high accuracy. This situation is not desirable in a lab situation because the “high” accuracy may simply be random chance and not a true indicator of good measuring skill. d. The darts are grouped together and have hit the bulls-eye. This demonstrates high precision and high accuracy. Scientists always strive to maximize both in their measurements. FIGURE 1.2 Students in a chemistry lab are making careful measurements with a series of volumetric flasks. Accuracy and precision are critical in every experiment. Summary • Accuracy is a measure of how close a measurement is to the correct or accepted value of the quantity being measured. • Precision is a measure of how close a series of measurements are to one another. Practice Take the quiz at the link below: 2 www.ck12.org Concept 1. Accuracy and Precision http://www.quia.com/quiz/1863743.html?AP_rand=980502951 Review 1. Define accuracy. 2. Define precision. 3. What can be said about the reproducibility of precise values? • accuracy: A measure of how close a measurement is to the correct or accepted value of the quantity being measured • precision: A measure of how close a series of measurements are to one another. Precise measurements are highly reproducible, even if the measurements are not near the correct value. References 1. Daniel Arizpe. http://commons.wikimedia.org/wiki/File:High_school_basketball_game.jpg. Public Domain 2. CK-12 Foundation - Christopher Auyeung. CC-BY-NC-SA 3.0 3. Image copyright zebrik, 2012. http://www.shutterstock.com. Used under license from Shutterstock.com 3.
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