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Additional Measures of Center and Spread

Additional Measures of Center and Spread. Math Alliance Fall 2011. Measures of Center. Mode Most frequent value Mean Fair share or balance point Median If odd number of values then middle number If even number of values then mean of middle two numbers. Five Number Summary.

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Additional Measures of Center and Spread

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  1. Additional Measures of Center and Spread Math Alliance Fall 2011

  2. Measures of Center Mode Most frequent value Mean Fair share or balance point Median If odd number of values then middle number If even number of values then mean of middle two numbers

  3. Five Number Summary Minimum: lowest value 1st Quartile: median of the lower half Median: middle number 3rd Quartile: median of the upper half Maximum: highest value

  4. Box Plot Graph of the five number summary

  5. Interpretation of Box Plots The five number summary divides a data distribution into 4 parts. About what percent of the data values in each of the following intervals? • before the median • after the median • in the box (between the 1st and 3rd quartiles) • before the upper quartile • after the upper quartile • before the lower quartile • after the lower quartile • between median and upper quartile • between the median and the lower quartile

  6. Definition of outliers Steps to determine if there are outliers: • Find the Interquartile range (IQR) IQR = Q3 – Q1 • Multiply: 1.5 * IQR • Add: Q3 + 1.5*IQR • Any value greater than Q3+ 1.5*IQR is an outlier • Subtract Q1 – 1.5*IQR • Any value less than Q1-1.5*IQR is an outlier

  7. Definition of Outlier Any value more than 1.5 IQRs above Q3 or below Q1. Or Any value more than 1.5 “boxes” above Q3 or below Q1 Example: Natural Peanut Butter Quality Ratings: 34 40 52 57 57 60 60 63 67 69 69 69 71 89 Find the 5 number summary Make a box plot Determine if there are any outliers

  8. Comparing two or more Groups Side by side box plots Calories for all beef hot dogs: 157 149 131 111 149 152 190 184 175 190 139 181 148 176 158 132 141 186 135 153 Calories for all poultry hot dogs: 170 152 146 142 102 135 94 106 86 113 102 143 99 132 144 129 87

  9. Comparing two groups Each each type of hot dog • Find the 5 number summary • Construct a box plot of each using the same scale for both. Place the beef hot dog box plot above the poultry hot dog box plot. • What type of hot dog has the fewer number of calories? Use the box plots and the percent to explain your answer.

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