3/2003 Rev 1 I.2.11 – slide 1 of 11 Session I.2.11 Part I Review of Fundamentals Module 2Basic Physics and Mathematics Used in Radiation Protection Session 11Basic Statistics IAEA Post Graduate Educational Course Radiation Protection and Safety of Radiation Sources

3/2003 Rev 1 I.2.11 – slide 2 of 11 Upon completion of this section the student should be able to demonstrate an understanding of the following statistical concepts: Upon completion of this section the student should be able to demonstrate an understanding of the following statistical concepts: Precision and Precision and Accuracy Accuracy Objectives

3/2003 Rev 1 I.2.11 – slide 3 of 11 Precision Precision is an indication of how close the elements of a series of measurements are to each other. Precision is an indication of how close the elements of a series of measurements are to each other. It is desirable to have results that are precise, the results are grouped close together and not scattered. It is desirable to have results that are precise, the results are grouped close together and not scattered.

3/2003 Rev 1 I.2.11 – slide 4 of 11 Precision Good Precision

3/2003 Rev 1 I.2.11 – slide 5 of 11 Precision Poor Precision

3/2003 Rev 1 I.2.11 – slide 6 of 11 Accuracy is a measure of the difference between a measured value and the true value, that is, a measure of the error. Accuracy is a measure of the difference between a measured value and the true value, that is, a measure of the error. If the errors of measurement average to zero, then the system is said to be accurate. If the errors of measurement average to zero, then the system is said to be accurate. It is desirable to have a system that is accurate, that is, has results that are close to the true value. It is desirable to have a system that is accurate, that is, has results that are close to the true value. Accuracy

3/2003 Rev 1 I.2.11 – slide 7 of 11 Accuracy Good Accuracy

3/2003 Rev 1 I.2.11 – slide 8 of 11 Accuracy Poor Accuracy

3/2003 Rev 1 I.2.11 – slide 9 of 11 Precision and Accuracy A system may be precise even though it is not accurate. A system may be precise even though it is not accurate. Conversely, a system may be accurate, but not precise. Conversely, a system may be accurate, but not precise.

3/2003 Rev 1 I.2.11 – slide 10 of 11 Precision and Accuracy Good Precision Good Accuracy

3/2003 Rev 1 I.2.11 – slide 11 of 11 Precision and Accuracy Possible Results Good Precision PoorPrecision GoodAccuracyPreciseandAccurateImprecisebutAccurate Poor Accuracy PrecisebutInaccurateImpreciseandInaccurate