Displaying Data

Engineering Statistics - STAT3115 - 23 January 2018

Stem-and-Leaf Displays

  • For numerical data (not categories)
  • Original data can be recovered
  • Instructions:
    1. Select one or more leading digits for the stem values (5-20 stems is recommended)
    2. Remaining digits are the leaves
    3. List the possible stem values (in decreasing order) in a vertical column
    4. Draw a vertical lie to the the right
  • Data received from Stem-and-Leaf:
    • Typical or representative Value
    • Spread about the typical value
    • Gaps
    • Symmetry
      • symmetric
      • bimodal
      • right (positively) skewed
      • left (negatively) skewed
    • Number of locations or peaks
    • Presence of outlying data

Dotplots

  • Good for small data sets or when there are few distinct values (lots of repeats)
  • Better to use histograms for larger data sets

Histograms

A bar plot

  • Each data value can be:
    • Numerical or Quantitative
    • Categorial or Qualitative