Boxplots

Boxplots - Why use boxplots? ease of construction...

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Why use boxplots? ease of construction convenient handling of outliers construction is not subjective (like histograms) Used with medium or large size data sets (n > 10) useful for comparative displays
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Disadvantage of boxplots does not retain the individual observations should not be used with small data sets (n < 10)
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Modified boxplots display outliers fences mark off mild & extreme outliers whiskers extend to largest (smallest) data value inside the fence ALWAYS use modified boxplots in this class!!!
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Inner fence Q1 Q3 Q3 + 1.5IQR Any observation outside this fence is an outlier! Put a dot for the outliers. Interquartile Range (IQR) – is the range (length) of the box Q3 - Q1
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Modified Boxplot . . . Q1 Q3 Draw the “whisker” from the quartiles to the observation that is within the fence!
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A report from the U.S. Department of Justice gave the following percent increase in federal prison populations in 20 northeastern & mid-western states in 1999. 5.9 1.3 5.0
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This note was uploaded on 12/09/2011 for the course STATS 221 taught by Professor Nielson during the Fall '10 term at BYU.

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Boxplots - Why use boxplots? ease of construction...

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