Day 04: Statistics for Business Applications

• Last Time:
  • qualities of histograms
    • symmetry
    • unimodal, bimodal, or multimodeal?
    • What are typical (central) values?
    • What are the largest and smallest values?
    • Are there unusual or atypical values?
  • measures of central tendency
    • mean - average value (center of mass of histogram)
    • median - middle value
    • mode - most common value (or class midpoint)

• Today:
  • Problems with data for 2.3, #25? I've obtained a corrected data file (ASCII or Excel format only!)

  • Collect Homework #2 (you can turn it in as late as Monday noon - but make sure that you include sections 2.1-2.3; also, note that you should have used our directions on the problem rather than those in the book!)

    More on histogram bin width: a neat web demo

  • Sorry I don't have your first homework back yet.

  • Do you have any questions about the homework associated with 4.1-4.2? (Due Tuesday!)

  • Chapter 4: measures of spread
    • Example: M&Ms

    • range

      Difference between largest and smallest values

    • variance

      • mean of the squared deviations (differences from the mean) of the data.
      • Notation - population variance (sigma squared) versus sample variance

    • standard deviation

      square root of the variance - it has the same units as the mean

    • Computing means, standard deviations, etc. with Minitab:

      Stat -> Basic Statistics -> Display Descriptive Statistics
      

    • The empirical rule - the 68/95/99 rule.

• Next time:
  • Homework #3 due (section 4.1-4.2)
  • finish measure of spread (standard deviation), start normal distribution (the bell-shaped curve)

Links:

• A web demo of the measures of central tendency
• Another bin-width demonstration