Lesson 2: Data Distributions with Stemplots and Dotplots

August 26, 2026

Review:

Presentation:

  • Data Distributions
    • The “shape” of the data
    • Distribution of Exam Scores
    • Types of common distributions
      • Normal Distribution: A symmetric bell-shaped curve, where most data points cluster around the mean.
      • Uniform Distribution: A flat distribution, where all outcomes are equally likely.
      • Skewed Distribution (Right or Left Skewed): A distribution with a longer tail on the right or left.
      • Bimodal Distribution: A distribution with two distinct peaks, showing two different groups within the data.
    • Visualize the distribution of data you want to understand
      • Picture is worth a thousand words
      • Not much training necessary to look at a data graphic
      • Improved approach for detecting “patterns” and inviting “participation“
      • Use stemplots for small datasets
  • Dotplots
    • Demonstrate dotplot construction using sleep hours
    • Rules for making dotplots
      • Keep rows and columns neatly aligned
      • Clearly label horizontal axis and vertical axis
      • Try to make each “dot” (circle) the same size
  • Stemplots (aka Stem and Leaf plots)
    • Against All Odds Video – Unit 2 (06:00-11:00) – setup military uniform example
    • Demonstrate stemplot construction using student height and/or hours worked data
    • Rules for making stemplots
      • Keep rows and columns neatly aligned
      • Don’t use commas, decimals or other visible separators
      • Display gaps in data with empty space

Activity:

Justin

Justin Holman is CEO of Aftermarket Analytics, where he leads efforts to develop cutting edge sales forecasting and inventory optimization technology for the Automotive Aftermarket. Prior to joining Aftermarket Analytics, Justin managed corporate consulting for the Strategy & Analytics division at MapInfo Corporation, leading major projects for retail clients including The Home Depot, Darden Restaurants, Bridgestone-Firestone, Sainsbury’s and New York & Company. Before that, Justin served as Vice President of Software Development at LogicTools, now part of IBM's supply chain application software group. Justin holds a B.A. from Claremont McKenna College, a Ph.D. from the University of Oregon and an Executive Management certificate from Northwestern University's Kellogg School of Management.

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