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Unit 2: Some Basics

Unit 2: Some Basics. Example: Hair color at NYS Fair. Numerical variables: Graphs of frequencies I. dot plots stem-and-leaf plots Ex: 79, 91, 59, 52, 94, 74, 75, 87, 67, 35, 91, 89, 96, 92, 92. Numerical variables: Graphs of frequencies II. histogram

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Unit 2: Some Basics

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  1. Unit 2: Some Basics

  2. Example: Hair color at NYS Fair

  3. Numerical variables: Graphs of frequencies I • dot plots • stem-and-leaf plots • Ex: 79, 91, 59, 52, 94, 74, 75, 87, 67, 35, 91, 89, 96, 92, 92

  4. Numerical variables: Graphs of frequencies II • histogram • 79, 91, 59, 52, 94, 74, 75, 87, 67, 35, 91, 89, 96, 92, 92 • (Note similarity to dotplot and stem-and-leaf plot) • Excel’s “histograms” aren’t, unless bar widths are equal

  5. Density scale • Weekly salaries in a company • Vertical axis is in % per $200 • Where is the high point?

  6. Reading a histogram: Hrs slept by CU students(Data from questionnaire) Which given interval contains the most students? Which 1-hr period contains the most students (i.e., is most “crowded”)? About what % slept 8 hr? About what % slept 3 or 4 hr? If there were 240 surveyed, about how many slept 6-7 hr? Sum= 20 So maybe 5% slept 1hr, 5% 2hr and 5% 3hr; Or maybe 0% slept 1hr, 7% 2hr, 8% 3hr

  7. Drawing a histogram:Horses’ weights in kg Sum = 250

  8. Frequencies by area?

  9. Weekly salaries in a small factory: 30 workers 17 $200, 5 $400, 6 $500, 1 $2000, 1 $4600 avg = $500, median = $200

  10. Box-&-whisker plots • Uses all of min, first quartile, median, third quartile, max • “Normal” just shows them all • “Modified” puts limit on whisker length -- 1.5 IQR • 3rd quartile +1.5 IQR = “(inner) fence” • whisker ends at last value before or on fence • beyond the fence is an “outlier” • reject only “for cause” (?) • beyond 3rd quartile + 3 IQR (“outer fence” or “bound”) is “extreme outlier”

  11. Normal: Modified:

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