Frequency Distribution 2011, 9, 22

Lecture Topics  Frequency distribution table*  Frequency distribution graphs*  Shape of a distribution

Need Your  Number of out-of-state trips in last 12 months?  Distribution of a variable: A summary of all the different values of a variable  Descriptive statistics: Statistical tools/procedures to help organize, summarize, and simplify a large set of data

Frequency Distribution Table Frequency Distribution Table Value – X (n=20) Tallyll llll llll ll lll ll l lFrequency (f) Proportion (P =f/n) Percentage (%= px100) 10% 20% 35% 15% 10% 5% 5%5%5%5% Cumulative % (c% ) 100% 90% 70% 35% 20% 10% 5%

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Frequency Distribution Table (n = 30) Class Interval fp%c% A (90-100) %100% B (80-89) %76.5% C (70-79) %16.5% D (60-69) 1.033%3.2% Xfp%c% % % % % % % % % % % % %3.2 Grouped Frequency Distribution Table

Frequency Distribution Graphs Line Graph  All start with 2 perpendicular lines called axes –Horizontal line: The X-axis indicates values (scores) –Vertical line: The Y-axis indicates frequencies

 Histogram: A bar type graph for continuous data. No gaps between adjacent bars  Bar Graph: A bar-type graph for discrete variable. Gaps between adjacent bars. Outlier

Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the Wadsworth Group, a division of Thomson Learning Shape of a Distribution

Lecture Recap: Frequency Distribution  What is a distribution? What is descriptive statistics?  Table –Frequency distribution table –Grouped frequency distribution table  Graphs –Line graph –Histogram vs. Bar chart –Outliers  Shape of a distribution –Symmetrical –Positively skewed –Negatively skewed