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2_Descriptive Graphs_handouts

# 2_Descriptive Graphs_handouts - STAT 5615 Statistics in...

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1 STAT 5615 Statistics in Research (I) Descriptive Graphs Ott & Longnecker 3.3, 3.6

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2 Descriptive Statistics Objective: to summarize data Graphical Techniques - Pie charts - Bar charts - Histograms - Stem-and-Leaf plots - Time series plots - Boxplots Numerical Descriptive Techniques - Measures of Central Tendency - Measures of Variability
3 Types of Data Specific types of descriptive statistics are designed for specific types of data Continuous (Numerical) : values fall on a continuum Ex: height of a person; time to graduation; distance from home to work Discrete (Categorical) : values fall into distinct classes * Count : measures frequency of events Ex: # students in STAT 5615; # times a person flies in a year Note: sometimes this is treated as continuous variable * Nominal : values are named categories Ex: eye color; occupation * Binary : two-valued discrete data Ex: smoker or non-smoker; VA resident or not

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4 Discrete: (continued) * Ordinal : ordered discrete data. - Ordinal values are in order BUT you can not always define jumps/gaps between them. Ex: How would you rate the start of your semester? Complex: values have complex features. - much less commonly used. - more difficult to analyze quantitatively Ex: How do you draw a smiley face? :) :-) ^_^ Piece of cake No better / no worse than expected Painful
5 Graphical Statistics Graphical statistics provide visual descriptions of data, and form a basis for exploratory analysis. Types of diagrams: Relative frequency diagrams: Depict relative frequencies of fixed categories. Ex: Histograms, bar charts, pie charts, stem-and-leaf displays Main tool: relative frequency table Rank-based diagrams: Depict categories defined by ranking the data Ex: Stem-and-leaf displays, box-and-whisker plots Main tool: Percentiles

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