EX ST 222 Exam 1 Study Guide
Statistics in Everyday Life:
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Units
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Individuals
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Objects (people, animals, things) described by a set of data
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Variable
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Characteristic of units that can take different values for different units
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Example:
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Poll students
Student is the unit
Variable could be sex, major, age, GPR, height, opinion
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Population
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Set of all measurements of interest for a particular group
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When expressing a population you must express the variable and the
population of units
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Sample
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The subset of measurements from population of interest
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Samples must be random and representative
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Example:
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Ask registered voters if they agree with a certain issue
The population would be the opinions of all registered voters
The sample would be the opinions of selected registered voters
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Parameter
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A number calculated from a population
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The parameter is the true value
Ex: µ is the population mean
Ex: p is the population proportion
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Statistic
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A number calculated from a sample
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A statistic is an estimation of a parameter and is also called the point
estimate
X bar is the sample mean
S
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is the sample variation
S is the sample standard deviation
P^ is the sample proportion
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P and P Hat
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Are used for qualitative
P is the true proportion
P hat is the sample proportion
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X Bar and µ
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Used for quantitative
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µ is the true average
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X Bar is the sample average
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Observational studies
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Observe individuals and measure variables of interest
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No attempt is made to influence the responses
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Observer looks for patterns
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Purpose: describe some group or situation
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Sample surveys
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Type of study in which a selected group is surveyed because they
represent the entire group
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Type of observational study
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Ex: public opinion polls
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Census
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Type of study that attempts to include the entire population
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Don’t need statistics
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Experiments
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In observational studies just want to observe but not disrupt natural
behavior
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In experiments impose treatments and observe responses
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The purpose of the experiment is to study whether the treatment has an
effect on the response
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Must have clearly defined goals before conducting the experiment
Statistics in Society:
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Everyone has an agenda, a motive
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 Fall '10
 ROSEMARTINEZDAWSON
 Sample standard deviation, representative

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