The Practice of Statistics Daniel S. Yates The Practice of Statistics Third Edition Chapter 1: Exploring Data Copyright © 2008 by W. H. Freeman & Company

Displaying Distributions with Graphs Categorical Data Quantitative or Numerical Data

Displaying categorical data

Displaying Categorical Data: Pie Charts Use a pie chart only when you want to emphasize each category's relation to the whole.

Displaying Categorical Data: Bar Graphs Easier to make and can be easier to read.

Displaying Numerical Data: Stemplots

Comparing Numerical Data: Back-to-back Stemplots Why stemplots? Stemplots give a quick picture of the shape of a distribution while including the actual numerical values.

Comparing Numerical Data: Back-to-back Stemplots What does this stemplot show us?

Comparing Numerical Data: Back-to-back Stemplots When might you not want to use a stemplot?

Stemplots: Split & Trim Statistical software called Minitab created this stemplot of the Virginia college tuition data.

Displaying quantitative data: Histograms Displays counts or percents Shows trend of data User defines number of classes Good for large data sets Does not display actual data values

Creating a histogram Divide data into ranges of equal width. Count the number of individuals in each class. Draw the histogram and label your axes.

Creating a histogram Divide data into ranges of equal width. The data ranges from 81 to 145, so starting with 75 with a width of 9 will work. Make sure each value falls in exactly one class.

Creating a histogram 2. Count the number of individuals in each class

Creating a histogram 3. Draw the histogram using counts or percentages and label your axes.

Be sure to choose classes all the same width. Histogram Tips Be sure to choose classes all the same width. Use your judgment in choosing classes to display the shape. Too few classes will give a 'skyskaper' graph; two many will produce a 'pancake' graph. Beware of letting statistical sotware and graphing calculators choose the classes for you. Histograms that display counts are often called frequency tables. Histograms of percents are good for comparing several distributions with different numbers of observations.

Histograms verses bar graphs When would you use either a histogram or bar graph?

Examining a distribution Shape unimodal or bimodal Symmetric or skewed right or left Center Midpoint Spread Range Outliers?

Examining a distribution Shape unimodal or bimodal Symmetric or skewed right or left Center Midpoint Spread Range Outliers?

Dealing with outliers Electrical Components