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Chapters 3 and 4 Notes (Student)
1
What Do Samples Tell Us?
• Does the number describe a sample or a population?
• Parameter
– a number that describes the population.
It’s a fixed number, but we usually don’t know its
value.
• Statistic
– a number that describes a sample.
Its value
is computed from sample information, but it can
change from sample to sample.
The Big Picture
Population
Sample
Statistic
Parameter
select
estimate
calculate
describes
True proportion
True mean
Sample proportion
Sample mean
Error in Estimation
• We wish to estimate a parameter from a statistic.
•B
i
a
s
– consistent, repeated deviation of the sample
statistic from the population parameter in the same
direction when we take many samples.
• Variability
– describes how spread out the values of
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View Full Document Chapters 3 and 4 Notes (Student)
2
Managing Bias and Variability
• To reduce bias, use random sampling.
Produces
unbiased estimates of the parameter.
• To reduce the variability of a SRS, use a larger
sample.
Bias and Variability
Margin of Error
• A statistic, calculated from a random sample, will
usually not estimate the parameter exactly.
• Surveys often report a percentage and a “margin of
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This note was uploaded on 02/14/2011 for the course STAT 110 taught by Professor Johnson during the Fall '07 term at South Carolina.
 Fall '07
 JOHNSON
 Statistics

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