The Basic Practice of Statistics David S. Moore The Basic Practice of Statistics Fourth Edition Chapter 1: Picturing Distributions with Graphs Copyright © 2007 by W. H. Freeman & Company
Statistics – The study of how to collect, organize, analyze and interpret numerical information from data for the purpose of making decisions.
Important aspects of any graphical representation are Shape, Center, Spread.
Graphs such as bar charts or pie charts help display the distribution of a variable
Dot plots Does not have to begin at zero. Should cover the range of values.
Groups data into classes. Histogram Classes 15< % adults with bachelors degree < 20 20< “ <25 25< <30 30< <35 35< <40 40< <45 Groups data into classes. You can choose classes but must do so carefully.
symmetric Skewed right
Used for small data sets. Presents more detail. All data is displayed
Measurements of Center
The mean is nonresistant (changed) to extreme observations or outliers; while the median is resistant (not changed). Mean Median Mean and median are the same
Measuring Spread Range Measuring center alone can be misleading. Often the spread or variability of the data is very important. Range The difference between the largest and smallest observations.
Example: odd # of Observations 4 6 7 8 12 17 20 31 38 40 52 Q3 Q1 M even # of Observations 4 6 7 8 12 17 20 31 38 40 Q1 14.5 Q3
Properties of Standard deviation measures spread about the mean. Should only be used when the mean is the measure of center. s = 0; only when there is no spread, all observations are exactly the same. s is large; values are very spread out. s is small; values are clustered close to the mean. s is nonresistant likex (mean); strongly influenced by extreme observations or outliers.