• purpose (to find-out)

    • phenomenon (group characteristics)
    • reason-result (relationship of factotrs)
    • economic, social tendencies(, rules)
      • used for predicting future, and helping decision

  • how

    • survey
    • experiment
    • observation

  • terms

    • unit
      • person
      • state
      • food
      • …
    • case (record)
    • variable

  • level of measurement (scale of measure)

    • nominal scale : identifying use
    • ordinal scale : serial ordering use
    • interval scale : scoring use
    • ratio scale : ratio use

  • data

    • value’s level
      • qualitaive value
      • quantitative value
    • value’s quantity
      • single-meaning value
      • multi-meaning values

  • data, information repository

  • center tendency

    • mean 
      1

      mean(data)
    • trimmed mean 
      1

      mean(data, trim=0.10)
    • median 
      1

      median(data)
    • mode 
      1

      mode(data)

  • dispersion

    1

    summary(data)
    • variance
    • standard deviation 
      1

      sd(data)
    • range
    • coefficient of variation
    • quartile deviation
      • interquartile range : Q3 - Q1
      1
2

      IQR(data)
quantile(data, probs=c(0.25, 0.5, 0.75))  //it's quaNtile, not quaRtile

  • continuous data graph

    • histogram 
      1
2

      a = rnorm(200)
hist(a, col="RED")
    • stem-and-leaf 
      1
2

      stem(data)
stem(data, scale=2)
    • box plot 
      1

      boxplot(data)
      • five-number-summary -adjacent value

  • web tool