Statistics in a Nutshell

Interested in Entire Population Large Population = Expensive Surveys Sample a Small Group

– Infer Population Characteristics– from Sample Characteristics

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

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

Sampling

Sampling is faster, cheaper, easier.

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.

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 !

Statistics

Descriptive Statistics– Collecting and Analyzing Data– “Tells a story about the numbers”

Inferential Statistics– Drawing conclusions about a population

Descriptive Statistics

Measures of Central tendency– Mean (Arithmetic Average)– Median (Middle Value)

Measures of Variation– Variance– Standard Deviation

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

Important Statistics

Mean– Tells where the data is centered

Standard Deviation– Tells how far the data is spread out

Family Reunion

Babies, youngsters, teenagers

young adults, middle-aged parents

grandparents, great grandparents

Average Age ?????

Standard Deviation ?????

15th High School Reunion

Average Age ?????

Standard Deviation ?????