and Cautions What is Random Random Drawing from a hat Rolling a die Using a number generator Not Random Picking randomly First one toraise their hand do a task etc Why Random ID: 235526
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Slide1
Sampling Methodsand CautionsSlide2
What is Random?
Random:
Drawing from a hat
Rolling a die
Using a number generator
Not Random:
“Picking” randomly
First one to…(raise their hand, do a task, etc.)Slide3
Why Random?
Everyone has an equal chance of being selected
Helps to reduce bias by eliminating the human factor of selection
Helps to account for the variability between people (even when we don’t know it’s there)Slide4
Types of Random Selection
Simple Random Sample: Everyone gets a number and is selected via a random number generatorSlide5
Types of Random Selection
Stratified Random Sample: The population is broken up into strata (Male/Female, Freshmen/Sophomore/Junior/Senior) and a certain number of people are randomly selected from each strata.Slide6
Types of Random Selection
Systematic Random Sample: A random number generator is selected to pick a person from 1-X. Each
X
th
person is then selected after that.
For example, a die is used to select a number 1-6. Let’s say it comes up a 2. The second person would be selected for the experiment, and then the 8
th
, and then the 14
th
, continuing by 6.Slide7
Types of Random Selection
Cluster Sampling: Choosing random clusters of subjects.
Pickings pairs of Husband/Wife, Father/
Dauther
, entire families, neighborhoods, etc.Slide8
Types of Random Selection
Convenience Sampling: “randomly,” or randomly choosing those conveniently close to survey.
Surveyors at the mall, how we’ve surveyed so far (in the classroom), asking friends or neighborsSlide9
Population of Interest
We always want to ask ourselves: Who is this generalizing to?
If we take the heights of our class, are we trying to generalize to AP Stats students? To Juniors and Seniors at HSHS? To the school? To the county, the state, the country…? What is the population of interest?Slide10
BiasBias is bad, yet unavoidable. We seek to reduce bias.Slide11
Types of Bias
Selection Bias: When the researcher actively creates a bias in the way they select their subjects.
Undercoverage
Non-randomSlide12
Types of Bias
Response Bias
Non-response
Voluntary ResponseSlide13
Types of Bias
Anything else that might throw off the data
Using a placebo unnecessarily
Not using a placebo when one should
Not utilizing blind or double-blind methods when appropriate
Etc.Slide14
Random Digit Table