Unit 2

Types of samples:

Convenience sample, voluntary response sample, simple random sample, stratified random sample, cluster random sample

Why do people use convenience samples?

Easy to reach

What happens during voluntary response samples?

People choose to reply

What can convenience sample and voluntary response lead to?

Bias

Procedure for simple random sample:

Assign numbers → random number generator → select

Write names on slips of paper → shuffle names in hat → select

How to take stratified random sample?

Split population into strata → choose SRS from each strata

What does the individuals in each strata have?

Shared attributes or characteristics

What kind of grouping is stratified random sampling?

Homogeneous

When does a sampling method produce the best estimates?

If have low bias and low variability

A number that describes an entire population:

Parameter

A number that describes a sample:

Statistic

In a stratified random sample, we sample ______ from ______

Some from all groups

In a cluster random sample, are groups homogeneous or heterogeneous?

Heterogeneous

In a cluster random sample, we sample ______ from ______

All from some groups

How to conduct a systematic random sample?

Choose random starting point and use equal intervals

Some people are less likely to be chosen:

Undercoverage

Examples of undercoverage:

Calling landlines, surveying homeowners

People can’t be reached or refuse to answer:

Nonresponse

Examples of nonresponse bias:

People don’t answer or hang up phone call

What problems does response bias involve?

Problems in data gathering instrument or process

Examples of response biases:

People lying, working of question

What type of bias is about people lying when answering survey?

Self reported response bias

In observational studies, can you say that explanatory variable caused response variable?

No

In observational studies, why can’t you say that explanatory variable caused response variable?

There may be confounding variable

What is the confounding variable related to?

Explanatory variable

What does confounding variable influence?

Response variable

Are treatments imposed in observational studies?

No

Are treatments imposed in experiments?

Yes

What do experiments allow us to show?

Causation

What/who treatment is imposed on:

Experimental units

What is done (or not done) to experimental units:

Treatments