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Chapter 10

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Simon Fraser University
STAT 100
Wendell Challenger

Chapter 10 Descriptive Statistics  Statistics has developed a variety of tools for collecting and understanding data  So far we have discussed ways to collect data  So how do we deal with the data we collect? - Begin by summarizing the data - Want to describe or summarize in a clear and concise way - Will first focus on descriptive statistics (graphical and numeric) Recall…  Interested in something about a population  Population is a collection of individuals  Describe individuals with data  Data sets contain information/facts relating to individuals  Variables are attributes of an individual - E.g., hair color, pain severity…  Distribution of a variable tell us what value a variable can take and how often it will take these values Types of Variables  Two main types of variables: 1. Quantitative Variables - Take on numeric values for which addition and averaging make sense (height, weight, income…) 2. Categorical Variables - Each individual falls into a category. Ethnicity, male/female, success/fail - Ordinal data is a special type of categorical data where categories have ordered in a natural way. Rate your preference for this course from 1(dislike) to 5 (enjoy greatly) Descriptive Statistics  Numerical: Summary Tables  Graphical: Bar Graphs, Pie Charts Graphical Descriptions of Data  Pictures (graphics) can be a powerful tool for summarizing data.  A graph (or graphic) is any visual display of numbers  Data visualization is still an emerging field  Many different types of plots are used  The goal of a graph is to - Summarize information from a data set into a picture that is easy to understand, but accurate - Often used to highlight a specific feature of the data Recall…  Data are values of variables that we observe in a sample  Sample was drawn from a population  We are trying to find out about something about the values of the variable in the population. We want to make an inference about the population with the data. Data Distributions  Distribution of a variable gives the values the variable can take and how often it takes on each value - Population distribution is a distribution for a population of values. Also called a probability distribution. - An empirical distribution is a distribution of a sample. Our grades - We use summaries of an empirical distribution to learn about a population distribution Data Distributions  For categorical data, we can summarize the distribution easily: 1. Identify all of the values the variable can take 2. Count the number of times each value is observed 3. Count
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