Displaying and describing quantitative data

Displaying and describing quantitative data

1. Displaying quantitative variables

   • Histogram
     • like a bar chart
     • no gaps
       • gaps=no value
     • choose the width of the bins
   • Stem-and-Leaf Displays
     • like Histogram
     • give individual values
       • breaks each number in 2 parts

2. Distribution

   • Mode
     • single, most frequent value
     • describe shape of distribution
     • types
       • unimodal
         • one main hump
       • bimodal
         • 2 humps
       • multimodal
         • 3 or more humps
       • uniform
         • no mode
   • Shape
     • Symmetry
       • tails
         • thinner ends
       • skewed distribution
         • to side of longer tail
     • Outliers
   • Center
     • mean
     • median
       • 2 equal areas
   • Spread
     • range
       • max-min
     • IQR
       • interquartile range
         • IQR=Q3-Q1
     • standard deviations
       • variance
         • average of squared deviation
         • square root

3. Summarizing distribution

   • boxplot
   • five number summary