Stats 024 - Statistics 024B 1 Stats 024b 001 Monday NCB 114...

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Stats 024b 001 Monday NCB 114 , Wednesday and Friday SSC 3022 11:30-12:30 Chapter 1: Picturing Distributions with Graphs January 7, 2008 Graphing Data The first thing you do in any statistical analysis is you graph it: gain insight on the data Individuals and Variables Individuals are the objects described by a set of data. Individuals may be people, but they may also be animals or things (Ex. Students, M&M’s, dogs, 2 by 4’s—also called an experimental unit or sampling unit depending on context) Variables are characteristics of an individual. A variable can take different values for different individuals (Ex. Age, Height, Grades, Colour, Weight, Breed, Breaking Strength) Types of Variables Quantitative Something that can be counted or measured for each individual and then added, subtracted, averaged etc, across individuals in the population Examples: how tall are you, your age, your blood cholesterol level, the number of credit cards you have Categorical Something that falls into one of several categories. What can be counted is the count or proportion of individuals in each category Examples: Your blood type (A, B, AB, O), your hair colour, your ethnicity, whether you paid income tax last tax year or not Distribution of the Variable The distribution of the variable tells us what values it takes and how often it takes these values. The values of a categorical variable are labels for the categories. The distribution of a categorical variable lists the categories and gives either the count or the percent of individuals who fall into each category. Distribution of a Categorical Variable Example 30% brown, 20% yellow and reds, 10% each of oranges, greens and tans Exploring Data 1. Begin by examining each variable by itself. Then move onto study the relationships among the variables 2. Begin with a graph or graphs. Then add numerical summaries of specific aspects of the data Bar Charts Used for categorical variables Gives a visual display of the relative sizes of each category Pie Charts Used for categorical variables Statistics 024B 1
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Gives a visual display of what fraction of the whole each category takes up Statistics 024B 2
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January 9, 2007 Histograms A graphical representation of a frequency distribution. The range of the variable is divided into class intervals for which the frequency of occurrence is represented by a rectangular column; the height of the column is proportional to the frequency of observations within the interval. Interpreting Histograms When describing a quantitative variable we look for the overall pattern and for striking deviations from that pattern. We can describe the overall pattern of a histogram by its shape, center and spread The object of the exercise is to take a large collection of data is to summarize it in a histogram to get the general look of the data
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This note was uploaded on 10/02/2008 for the course STATISTICS 024 taught by Professor Unknown during the Spring '07 term at UWO.

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Stats 024 - Statistics 024B 1 Stats 024b 001 Monday NCB 114...

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