Survey Sampling Methods - Lecture 1

1. Statistics 422 (Survey
Sampling Methods)
Monday, August 21, 2017
Dr. Marco Mesa-Frias, Department of Statistical Science,
University of Idaho
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2. What is Survey Sampling?
› Question: How do we observe something (i.e., survey) by
only observing part it (i.e., sampling).
What this Course is About
1. Design. How do we select a (proper) subset of things
from the set of all things according to goals and/or
constraints?
2. Inference. How do we use observations from some
things to make conclusions about all things?
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3. Statistical Inference
study participants,
fundamental units,
elements
Statistical inference
Underlying population
from which study
participants, elements or
units were drawn
Are study results representative of those from
infinitively large group of similar people or
elements?
The inference often takes the form of estimating
a population mean or proportion

4. Why sample?
› Advantages of Sampling
– reduced cost
– greater speed
– greater scope
– greater accuracy
› Disadvantages of Sampling
– loss of information
– requires technical expertise
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5. Basic Terminology of Sampling
› Element (𝜀𝑖)
› The fundamental unit on which measurements are made.
› Population (Ρ)
› The set of all elements of interest. e.g., Ρ = ቄ𝜀1, 𝜀2, 𝜀3, . . ሽ𝜀 𝑛
› Sampling Unit (U𝑖)
› Mutually exclusive sets of elements that are sampled together. e.g., 𝑈1 = 𝜀1, 𝜀2, ,
𝑈2 = 𝜀3 , 𝑈3 = 𝜀4, 𝜀5, 𝜀6,
› Sample (S)
› The set of the 𝑛 sampled/observed sampling units, and also the subset from Ρ of
sampled/observed elements. e.g., 𝑆 = 𝑈1, 𝑈2, , or 𝑆 = 𝜀1, 𝜀2, 𝜀3 , 𝜀4,
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6. Terminology Examples
› How many apples are on the trees in an orchard of 500
trees arranged in 50 rows of 10 trees each?
1. Select 𝑛 = 100 trees
2. Select 𝑛 = 10 rows of trees
3. Select
𝑛
50
= 2 trees from each row
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7. Basic Terminology of Sampling
› Sampling Frame
The list of all sampling units forming a population from which a sample is taken
(not necessarily the list of all elements in the population).
› Sampling Design
The process of how a sample (i.e., the set of n sampling units) is selected. This
includes (a) how we define the sampling frame and (b) how we decided which
sampling units we select.
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8. Types of Sampling procedures
Sampling
procedures
Probability
sampling
Simple Random
Sampling (SRS)
Systematic
Stratified
Cluster
Non-probability
sampling
Convenience,
Judgement,
Quota
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9. Probability Sampling
› Probability (Scientific) Sampling
A sampling design where every possible sample has a known probability of
being selected
› Non-Probability (Convenience/Volunteer) Sampling
A sampling design where the sample is selected by some non-random process,
implying a probability of 0 or 1 for some samples, or when sample selection
probabilities are unknown
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10. Probability Sampling
› Rationale of Probability Sampling
1. Obtain a representative sample.
2. Permit us to derive results about the error of estimation using probability
theory.
› Simple Random Sampling (SRS)
A sampling design where every possible sample of a specified n has an equal
probability of being selected
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11. THANK YOU…
Read Chapter 2 –Section
2.1 and Section 2.2
Elementary Survey
Sampling, 6th Edition
Textbook -
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