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:  Precision and  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.  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.  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. 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.  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