Probability and Statistics for Engineering and the Sciences (with Student Suite Online)

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Stat 321 – Day 3 Measures of Spread
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Announcements Lab questions? NHL: $209.78 MLB: $147.72 NFL: $322.82 NBA: $244.48 HW 1 (due Tuesday) questions? Reminder: Office Hour today 1-3
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Last Time – Measures of Center Mean = average all values But watch for outliers (not resistant) Median = “middle” observation “Typical” value Notes: “mode” usually not so useful with quantitative data Center may not be most relevant to study question Percentile = value with p% of data below it Median = 50 th percentile Lower fourth = 25 th percentile
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Last Time – “Test” for outliers 1.5f s criterion Any values more than 1.5 f s beyond lower fourth or upper fourth is flagged “Extreme” outlier if more than 3 f s away Modified boxplot
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Old Faithful inter-eruption time
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Example 1: Hypothetical Quiz  Scores Predictions Find the fourth spread for each class Median = 15 th observation = 5 points Lower fourth = median of bottom 15 observations = 8 th observation = 2 Upper fourth = 8 Fourth spread = 6
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