This document discusses population and sampling methods in research. It defines key terms like population, element, sample, and subject. It also explains different sampling techniques such as random sampling, stratified sampling, cluster sampling, and non-probability sampling methods like convenience sampling, quota sampling, and judgmental sampling. The document outlines advantages and disadvantages of each sampling method and notes that determining an appropriate sample size is important for making valid statistical inferences about a population.
2. Population and Element; Sample and
Subject
Population:
The entire group under study as defined by research
objectives
Element:
An element is the single member of the population
Sample:
A sample is a subset of the population that should
represent the entire group.
Subject:
A subject is the single member of the sample (Just as element
is a single member of the population)
3. Sampling is the process of selectingobservations
(a sample) to provide all information about of
the population.
Sample
It is aunit that is selected from
population
Represents the whole population
Sampling Frame
Listing of population from which asample ischosen
9. All subsets of the frame are given an equa
l
probability.
Random number generators
10. Population is divided into two or more groups
called strata
Subsamples are randomly selected from e
a
c
h
strata
11. Thepopulation is divided into subgroups (clusters) like
families.
Asimple random sample is taken from eachcluster
12. Order all units in the samplingframe
Then every number on the list isselected
N=Sampling Interval
13.
14. Theprobability of each casebeing selected from t
h
e
total population is not known.
Units of the sample are chosen on the basisof
personal judgment or convenience.
There are NOstatistical techniques for measuring
random sampling error in anon-probability sample.
16. Convenience sampling involves choosing respondents
at the convenience of theresearcher.
Advantages
Very low cost
Extensively used/understood
Disadvantages
Variability and bias cannot be measured or controlled
Projecting data beyond sample not justified
Restriction of Generalization.
17. Thepopulation is first segmented into mutually
exclusive sub-groups, just asin stratified sampling.
Advantages
Usedwhen research budget is limited
Very extensively used/understood
No need for list of populationelements
Disadvantages
Variability and bias cannot be measured/controlled
Time Consuming
Projecting data beyond sample not justified
18. Researcheremploys his or her own "expert”
judgment about.
Advantages
There is aassuranceof Quality response
Meet the specificobjective.
Disadvantages
Biasselection of sample mayoccur
Time consuming process.
19. Sample size determination is the act of
choosing the number of observations or replicates to
include in a statistical sample. The sample size is an
important feature of any empirical study in which the
goal is to make inferences about a population from a
sample. In practice, the sample size used in a study is
usually determined based on the cost, time, or
convenience of collecting the data, and the need for it
to offer sufficient statistical power.
Determination of sample size
Editor's Notes
Population refers to the entire group of people, events or things of interest that the researcher wishes to investigate. For instance, if a banker is interested in investigating the saving habits of blue collar workers in the pharmaceutical industry in Pakistan, then all blue collar workers in that industry throughout the country will form the population.
Element: In the above example, if there are 5000 blue collar workers happens to be the population of interest to a researcher, then each blue collar worker therein is an element.
Population Frame: the population frame is listing of all elements in the population from which the sample is drawn. For example, the payroll of an organization would serve as the population frame if its members are to be studied.
Likewise, a university registry containing a listing of all students, faculty, administrators, and support staff in the university during a particular academic year or semester could serve as the population frame for a study of the university population.
A roster of class students could be the population frame for the study of students in a class.
The telephone directory is also frequently used as a population frame for some types of studies.