04-08-2012, 03:43 PM
Probability Sampling
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Types of Probability Sampling Designs
Simple random sampling
Stratified sampling
Systematic sampling
Cluster (area) sampling
Multistage sampling
Simple Random Sampling
Objective: Select n units out of N such that every NCn has an equal chance.
Procedure: Use table of random numbers, computer random number generator or mechanical device.
Can sample with or without replacement.
f=n/N is the sampling fraction.
Stratified Sampling - Purposes
To insure representation of each strata, oversample smaller population groups.
Administrative convenience -- field offices.
Sampling problems may differ in each strata.
Increase precision (lower variance) if strata are homogeneous within (like blocking).