STAT 201 Chapter 2: Samples, Good & Bad
A politician takes out a TV ad asking constituents to call or write regarding their views on a newly proposed tax. This is an example of a(n) _____ response sample.
VOLUNTARY RESPONSE SAMPLE Since the individuals choose to put themselves in the sample
How do we choose a Simple Random Sample (SRS)?
We can choose a simple random sample (SRS) using random digits (found with software or with table of random digits)
What is Voluntary Response Sampling? What is an example of this?
When participants choose themselves by volunteering to respond Ex: Radio station asked listeners to call in to give their opinion
What is Convenience Sampling? What is an example of this?
When the researcher selects individuals who are easiest to reach Ex: student gave a survey to their roommates/people living around them
What are 2 types of biased sampling methods?
1) Convenience Sampling 2) Voluntary Response Sampling
What are 4 types of errors that can occur in our samples?
1) Undercoverage 2) Nonresponse 3) Response Bias 4) Question Wording Bias
What are the properties of random digits?
2 properties: 1) Each entry is equally likely to be any of the digits 0-9 2) The entries are independent of each other (no patterns)
What is a Simple Random Sample (SRS)?
A Simple Random Sample (SRS) consists of 'n' individuals from the population chosen in a way that every set of 'n' individuals is equally likely to be the sample ALLOWS IMPERSONAL CHANCE TO CHOOSE THE SAMPLE
A study is completed and the sample used was systematically better than the population. This particular study is _____ based on this information.
BIASED a biased study uses a sample that is not representative of the population
Asking drivers on campus whether or not finding a parking space is a problem as they try to enter a parking lot on campus is an example of a(n) __________ sample due to selecting individuals who are easiest to reach, generally resulting in bias.
CONVENIENCE sample is convenient to those asking the question, but they are only getting info from people attempting to park in one lot
What is a characteristic of a simple random sample that sets it apart from other samples?
Every sample of the same size has the same chance to be selected This is not true of most other sampling designs. In a stratified (by gender) sample of size n = 4, it is impossible to get a sample containing 2 males and 2 females, for example.
What does it mean if a sample is biased?
If a sample is biased, it systematically favors certain outcomes
Undercoverage
some people in population are not able to be in the sample
Nonresponse
when individuals in sample choose not to respond
Question Wording Bias
when the way a question is written/asked influences respondents to answer in a certain way
Response Bias
when there is a systematic pattern of incorrect responses
