Stats 3 Day 6
Do Now
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Check Homework
How to avoid bias…
1. Randomize
• 2. Sample Size
• 3. Sampling Techniques
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4 types of Sampling
1.
• 2.
• 3.
• 4.
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Simple Random Sample
Stratified Sampling
Cluster Sampling
Systematic Sampling
Simple Random
Sample (SRS)
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A simple random sample (SRS) is a sample
of size n where each set of n elements in
the population has an equal chance of
selection
Example: To do an SRS to survey patients
over 50 at Rush Hospital with high blood
pressure, assign numbers to each patient in
the population and use random number
table/random number generator
Stratified Sampling
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A design in which the population is divided
into several subpopulations (strata) and
random samples are drawn from each
subpopulation
Example: You want to ensure that each
class (freshmen, soph, juniors, and
seniors) are in the sample so you create a
stratum for each class and collect an equal
fraction of each for your sample
Cluster Sampling
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Split the population into similar parts
so that entire groups are chosen at
random
Example: group Pritzker students by
grade and then randomly choose a
grade
Systematic Sampling
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A sample is drawn by selecting an
individual based on a defined system
(like choosing every nth unit)
For a good sample, the system must
start at a random point and the list must
have no particular order
Example: survey every 10th student that
walks in the door
Determine the
Sampling Method
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Worksheet together
Determining the
Sampling Method
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Activity:
PUZZLES!
• Determine the Sampling Method
and the Bias
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Homework
Ch. 12 p.290
• #11-15
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