11-12-2012, 02:54 PM
SAMPLING METHODS
SAMPLING METHODS.ppt (Size: 665.5 KB / Downloads: 363)
LEARNING OBJECTIVES
Learn the reasons for sampling
Develop an understanding about different sampling methods
Distinguish between probability & non probability sampling
Discuss the relative advantages & disadvantages of each sampling methods
What is research?
“Scientific research is systematic, controlled, empirical, and critical investigation of natural phenomena guided by theory and hypotheses about the presumed relations among such phenomena.”
Kerlinger, 1986
Research is an organized and systematic way of finding answers to questions
Important Components of Empirical Research
Problem statement, research questions, purposes, benefits
Theory, assumptions, background literature
Variables and hypotheses
Operational definitions and measurement
Research design and methodology
Instrumentation, sampling
Data analysis
Conclusions, interpretations, recommendations
SAMPLING
A sample is “a smaller (but hopefully representative) collection of units from a population used to determine truths about that population” (Field, 2005)
Why sample?
Resources (time, money) and workload
Gives results with known accuracy that can be calculated mathematically
The sampling frame is the list from which the potential respondents are drawn
Registrar’s office
Class rosters
Must assess sampling frame errors
Process
The sampling process comprises several stages:
Defining the population of concern
Specifying a sampling frame, a set of items or events possible to measure
Specifying a sampling method for selecting items or events from the frame
Determining the sample size
Implementing the sampling plan
Sampling and data collecting
Reviewing the sampling process
Population definition…….
Note also that the population from which the sample is drawn may not be the same as the population about which we actually want information. Often there is large but not complete overlap between these two groups due to frame issues etc .
Sometimes they may be entirely separate - for instance, we might study rats in order to get a better understanding of human health, or we might study records from people born in 2008 in order to make predictions about people born in 2009.