1STAT 2000Sections 2.5-2.6Measures of Position Statistics: The Art and Science of Learning from DataAgresti-FranklinMeasures of PositionPercentilesThe pth percentile is the value below which you have p% of the data.Example: If a value lies at the 30thpercentile, then approximately 30% of the values are less than this value, and approximately 70% of the values are greater than this value.Notation: P30is the 30thpercentile.If John graduated at the 78th percentile in a class of 876, approximately how many students ranked below John?Joan learned that she would graduate ranked 47th (from the top) in a class of 876. Joan graduated at the _____ percentile of her class.Measures of Position: QuartilesQuartiles divide the data into 4 equal parts.25% | 25% | 25% | 25%Q1Q2 Q3Q1: First Quartile is the 25thpercentile.(25% below and 75% above)Q2: Second Quartile is the 50thpercentile. (50% below and 50% above)Q2 is also the median.Q3: Third Quartile is the 75thpercentile.(75% below and 25% above)25% | 25% | 25% | 25%Q1Q2 Q3P25P50P75medianD tFinding QuartilesFirst find the median. Then find the middle value of the upper and lower halves.Remember the data must be in order!Data:201930181722 Data2019301817 2223
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