1/20/2016

Types of Variables

• A quantitative variable is a variable that takes on numerical values for which arithmetic makes sense.
• A categorical or qualitative variable is a variable that records which category a person place or thing falls into.

Questions about data

• What variables are being measured?
• Are these variables appropriate for answering the question(s) of interest?
• What are the units of measurement?
• How are the data recorded?

Graphical Displays

• Why are graphing techniques useful?
  • Examine the overall shape of a distribution - (symmetric or skewed?)
  • Look for deviations from the overall shape - (unusual observations, gaps, etc.)
  • Locate the center of the distribution

Stem and Leaf Plots

• Separate each observation into a stem and a leaf.
• List the stems vertically in increasing order from top to bottom.
• Add the leaves (typically the last digit) to the right of the stems.

Histograms

• Divide the range of the data into classes of equal width.
• Count the number of observations in each class.
• Compute the relative frequency or percent for each class.
• Erect bars over each class interval.

Graphical Displays with R (Open p:\data\math\hartlaub\SportsStats\ReactionTimeS2016.csv)

• Your first R script - Open ReactionTime.R
• Stemplots - stem(x)
• Histograms - hist(x)
• Dotplots - dotchart(x)
• Bar Charts - barplot(counts)
• Pie Charts - pie(counts)

Comments and Questions on Chapter 1 Reading

• We will come back to this on Monday
• Textbooks are in!

Introduction to Simulation

• SRIS web site
• Statkey
• We will learn how to do simulation with R next week.

Class exercises - Getting comfortable with R

• Compare (graphically and numerically) the reaction times and pulses of women and men.
• Compare (graphically and numerically) the reaction times and pulses of different classes.
• Is the class in good shape? Create a variable and descriptive statistics to address this question.
• Replicate the simulation methods used in the examples for Chapter 1. Are your results exactly the same? Are your conclusions the same?

Reading Assignment - Please read Chapter 1 for class on Friday and Chapter 2 for class on Monday.