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Sampling (Introduction (Advantages (Low cost, Fast Data Collection),…
Sampling
Introduction
Definition
Selection
Of a Subset of Individuals
Of Part of a Population
Of a Sample
Used to
Estimate
Characteristics of a Whole Population
Advantages
Low cost
Fast Data Collection
Widely Used in
Business Researches
Medical Researches
First Stage
Define
Population of Concern
Batch
Straightforward Population
In a Period
In Occasions
'Superpopulation'
Phenomenons
Rats
Second Stage
Specify
Sampling Frame
Probability Sample
Every Unit Has a Chance to Be Select
Avoid
Biased Estimates
Nonprobability Sample
Some Elements
With No Chance of Selection
With Replacement
Elements Can Be Select More than One Time
Scientists Collecting Fishes
After Fished
The Fish is Put Again in the Water
Without Replacement
Elements Can Be Select Only Once
Third Stage
Specify
Sampling Method
Stratified Sampling
General Description
Population Divided
In Strata
Each Stratum
Has a Sample
Every Element
In Only One Stratum/Subpopulation
Widely Used in
Political Survey
Types
With Optimum Allocation
Strata with Equal Numbers of Elements
With Proportionate Allocation
Number of Elements in Each Stratum
Proportional to it Size
Statistical Measures
Standard Error
?
Sum of All Stratum Sizes
Count of Strata
h = Stratum Number
Stratum Size
Sample Mean of Stratum
Number of Observations in Stratum
Sample Standard Deviation of Stratum
Sample Mean
Sum of All Stratum Sizes
Count of Strata
Stratum Size
h = Stratum Number
Sample Mean of Stratum
Most Effective When
Variability within Strata
Is Minimized
Variability between Strata
Is Maximized
Variable Related with Stratification
Is Correlated
With Desired Variable
Less Effective When
Too Expensive
There Is No Homogeneus Stratum
Simple Random Sampling
Uniforme Distribution
:forbidden:
"Loaded Dice"
Equal Probability of Selection Design
Equal Probability
For Each Element
Don't Require Correction
Systematic Sampling
Ordered List
Of Elements
Selecting Elements
At Regular Intervals
Subsets of Same Size
With Different Selection Probabilities
Starting Point Is Not Automatically Selected
Used With
Some Streets
That Begin Poor/Rich
And Finish Rich/Por
Disadvantages
Vulnerable to Periodicites
Fourth Stage
Determine
Sample Size
https://en.wikipedia.org/wiki/Sample_size_determination
Sizes to Avoid
Too Big
When?
Smaller Samples Give Same Results
Law of Large Numbers
Short Definition
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Demonstration with Dice Roll
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Too Small
Fifth Stage
Implement
Sampling Plan
