Statistics in a Nutshell l Interested in Entire Population l Large Population = Expensive Surveys l Sample a Small Group –Infer Population Characteristics –from Sample Characteristics

Examples l Exit polls on election day l Marketing surveys for new products l Medical trials for new vaccines l Neilson ratings of television shows l 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 l Descriptive Statistics –Collecting and Analyzing Data –“Tells a story about the numbers” l Inferential Statistics –Drawing conclusions about a population

Descriptive Statistics l Measures of Central tendency –Mean (Arithmetic Average) –Median (Middle Value) l Measures of Variation –Variance –Standard Deviation

Measures of Central Tendency l Mean –Arithmetic Average –Balance Point –Basis for other statistics –Influenced by extremes l Median –Middle Value –Different Balance Point –Not influenced by extremes

Important Statistics l Mean –Tells where the data is centered l 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 ?????