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Statistics in a Nutshell
Interested in Entire Population Large Population = Expensive Surveys Sample a Small Group
– Infer Population Characteristics– from Sample Characteristics
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Examples
Exit polls on election day Marketing surveys for new products Medical trials for new vaccines Neilson ratings of television shows Air measurements for pollutants
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Definitions
Population --- Universe (Entire Group) Parameter
Numeric Characteristic of a Population Average, Variance, Standard Deviation, etc
Sample --- Subgroup of the Population Statistic
Numeric Characteristic of a Sample Average, Variance, Standard Deviation, etc
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Sampling
Sampling is faster, cheaper, easier.
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Sampling
Sampling is faster, cheaper, easier.
Hope, that the sample is representative of the
population; and therefore, the sample statistic
is an accurate estimate of the population
parameter.
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Sampling
Sampling is faster, cheaper, easier.
Hope, that the sample is representative of the
population; and therefore, the sample statistic
is an accurate estimate of the population
parameter.
If the sample is not representative of the
population, then all bets are off !
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Statistics
Descriptive Statistics– Collecting and Analyzing Data– “Tells a story about the numbers”
Inferential Statistics– Drawing conclusions about a population
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Descriptive Statistics
Measures of Central tendency– Mean (Arithmetic Average)– Median (Middle Value)
Measures of Variation– Variance– Standard Deviation
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Measures of Central Tendency
Mean– Arithmetic Average– Balance Point– Basis for other statistics– Influenced by extremes
Median– Middle Value– Different Balance Point– Not influenced by extremes
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Important Statistics
Mean– Tells where the data is centered
Standard Deviation– Tells how far the data is spread out
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Family Reunion
Babies, youngsters, teenagers
young adults, middle-aged parents
grandparents, great grandparents
Average Age ?????
Standard Deviation ?????
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15th High School Reunion
Average Age ?????
Standard Deviation ?????