AP STATS UNIT 4

Population

Entire group of individuals we want information about

Census

Collects data from every individual in the population

Sample

Subset of individuals in a population from which we actually collect data from

How to plan a sample survey?

Say exactly what population we want to describe

Say exactly what we want to measure

Decide how good a sample from the population is

Sample Survey

Studies that use an organized plan to choose a sample that represents some specific population.

Convenience Sample

Choosing individuals from a study that are easy to reach results

Unrepresentative Data is produced especially is we attempt to replicate 

Uses Bias

Bias 

The design of a statistical study shows this when it constantly overestimates or underestimates the value you want to know

What to do if your asked to describe how the design of a study leads to bias 

1. Identify a problem with the design 

2. Explain how this problem would overestimate or underestimate

Voluntary Response Sample

Consist of people who choose themselves by responding to a general invitation 

Usually not representative of some larger Popualtion of interest 

Often attracts people that feel strongly Abt an issue=bias

Random Sampling

Involves using a chance Proccess to determine which members of a population are incl in a sample 

Hat Method ()

Write the name of each of the participants on identical slips of paper, put the slips in a hat. mix them well and pull out slips one at a time until you have n of them

Not good if pop is LARGE

Simple Random Sample (SRS)

Of size n is chosen in such a way that every group of n individuals in the population has an equal chance to be selected for the sample 

Gives every possible sample/member of the desired size/population an equal chance to be included 

Stratified Random Sample 

Start by classifying the population into groups of similar individuals, called strata, Then choose a seperate SRS in each stratum and combine SRSs to form the sample 

“Some from all”

Cluster Sample

Classify the population into groups of individuals that are located near each other, called clusters. Then choose a SRS of clusters. All individuals in the choosen clusters are incl in the sample 

All from some

Works best when clusters look like the population but on a small scale

Inference

Infer information about the population from what we know about the sample 

Inference from voluntary or convenience=misleading bc these methods of choosing a sample are biased and on’t fairly represent the popualation 

Undercoverage

Occurs when some members of the population cannot be chosen in a sample 

Nonresponse

Occurs when an individual chosen for a sample can’t be contacted or refuses to participate