StatisticsPopulation/

SampleSurvey

Statistics

Practice of collecting and analyzing data to make future decisions.For example, Lays Potato Chips offers a wide variety of flavors http://www.fritolay.com/our-snacks/lays.html

Using sampling methods Lays surveys its population to determine which flavors will continue to be sold.

PopulationEvery element in the universe of interest;

all the possible football teams

SampleA subset of the population;

NFC East

SurveyQuestion asked of the sample group.

Who will win the Super Bowl?

Statistics is fun!

Population – every element in the universe of interestSample – a subset of the populationSurvey – question asked of the smaller group

Kinds of SamplesStatistics is still fun

Random

– Choose your population - 7th graders/7th grade teachers/7th grade parents.

– Put all the names in a hat and draw out 20 – this is your sample.

– Each is chosen by chance to answer the survey question.

– Considered unbiased because everyone has an equal chance of being chosen.

Is the BGT a good field trip for the 7th grade?

Stratified Random

– Same population divided into groups based on a common theme (7th grade students, 7th grade teachers, 7th grade parents). • No overlapping between groups• No group excluded

– Draw out 20 names from each group – this is your random sample to answer the survey question.

– Considered unbiased because everyone still has an equal chance of being chosen but every subgroup is included.

Is the BGT a good field trip for the 7th grade?

Cluster

- Same population divided into groups based on a common theme (7th grade students, 7th grade teachers, 7th grade parents). - Randomly pick one group.

Everyone in the subgroup is included. This is your sample that will answer the survey question.

- Considered biased because you have excluded two groups.

Is the BGT a good field trip for the 7th grade?

Systematic Random

– Same population - 7th graders/7th grade teachers/7th grade parents.

– Sample is based by choosing every ‘nth’ person. For example, every 8th person will answer the survey question.

– Still random but more constraints.

– Considered biased because one subgroup might be over or under represented.

Is the BGT a good field trip for the 7th grade?

Convenience

– Same population - 7th graders/7th grade teachers/7th grade parents.

– Sample is based on the individuals that are easiest to reach. For example survey question is asked during 1st lunch in the US cafeteria or during the 7th grade parent potluck dinner.

– Considered biased because one subgroup almost certainly will be over or under represented.

Is the BGT a good field trip for the 7th grade?

Voluntary Sample

– Same population - 7th graders/7th grade teachers/7th grade parents.

– Individuals choose to respond to the survey question. This is your sample.

– Considered biased because people with strong opinions respond.

Is the BGT a good field trip for the 7th grade?