selection of population and sampling technique
TRANSCRIPT
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SELECTION OF POPULATION AND
SAMPLING TECHNIQUE
The research generally prefers
a sample to a population frame
for a reason of:Economy of time
Effort
Cost
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POPULATION
Refers to the universe or the sum
total of all elements under
consideration. It is a larger group about which
your generalization is made.
Gay (1976) defines it as the groupto which a researcher would like
the results to be generalizable.
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SAMPLE
According to Ferguson (1976) any
sub-aggregate drawn from the
population, or it a portion of a
population.
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Kerlinger (1973) says, all members
of a well defined class of people,
events or objects, which is theactual statistical values and Its
characteristic are called
PARAMETERS
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Example of population frame;
All the TB patient with gastric ulcer inSan Lazaro Hospital.
All five-year-old children in the districtof Makati suffering from severe
diarrhea. All Nursing graduates of Perpetual
Help College Manila who passed the
board examination for the year 2012. Some population frame are either finite
or countable while others are infinitecan not be counted.
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Example of Finite Population
All patient with stomach ulcers in Makati medical
Center Patients who died of pneumonia in UST Hospital for
2000-2001.
All nurses who have gained employment abroad.
Sometimes what makes a population countable is that
it is delimited to a certain period of time or samplecan be derived. Ex. The number of nurses who passed
the
board exam is difficult to obtain, but it can be done,
hence population of all nurses who passed the boardexam is countable for a particular year desired. This
shows the importance of delimitation in the research.
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Example of Infinite Population
All cars that passed along Dapitan street All stars in the sky
All numbers of stone in the seashore.
Look at the examples of all cars that will pass
along Dapitan which can be counted, but
researcher who is very interested in the topic
may
decide to use a quota sample and take the first
100 or 200 cars that will pass along Dapitan
street.
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Factors Affecting in the
Selection of a Population
1. Objectives of the research
2. Availability of data
3. Nature of research
4. Variables to be measured, assessed
or associated
5.
Inferences to be made
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Some Minimum Acceptable
Sizes of Sample
Descriptive Research 10% of the
population for smaller population a
minimum of 20% may be required.
Correlational research 30 subjects
Ex post facto or casual comparative
research 15 subjects per group
Experimental research 15 subjects pergroup. Some authorities believes that 30
per group should be considered minimum.
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SAMPLING
A process which involves taking a part
of a population, making observation on
this representative group and thengeneralizing the findings to a bigger
population
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Slovin Formula to determine the
sample size of a population
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n = sample size
N = population sizee = the desired margin of error
Example:
Suppose the population has the size of 1000.what
size of the sample can be derived from it using a0.05
margin of error? Remember that the assumption of a normal
distribution of the population should beconsidered. When the normal approximation is
small or poor, this sample size formula does
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Sampling
Techniques/Strategies
The methods of deriving samples from
probability or nonprobability is called
sampling technique. There is therefore a
one-to-one correspondence between asample and a sampling technique or that
sample has its own unique sampling
technique.
There are two kinds of samples:
Probability sampletaken from one where
all elements in the population frame have
an equal chance of being selected.
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Nonprobabilityconsist of non-randomsample subjects. There is less chance ofobtaining a representative sample.
Different Types of Probability Samplesa. Random Samplinga method of selecting
sample size from a universe such that eachmembers of the population has an equal
chance of being selected as the sample. Thisstrategy is known as the best procedure.
Pre-requisite for Random Sampling:
1. Define the population
2. List all members of the population3. Select the sample by employing an adequate
procedure where every member has an equalchance.
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Two Basic Principles in Random Sampling
1. Equi-probabilitythis means that the member of
the population has an equal chances of being
included in the sample.
2. Independencerefers to the fact that when one
member is selected for the sampling this should
not affect the chances of the other members
getting choosen.
How it is being selected
1. Lottery Sampling or the fish bowl technique-this
procedure can be applied by first assigning
numbers to the participants of the populationassembling them in a sampling frame.
2. Table of Random Numbers-is the most systematic
technique for getting sample units at random.
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b. Systematic Sampling-it is a strategy for
selecting the members of the sample that
allows only chance and a system todetermine membership in the sample.
Systemis a planned strategy for selecting
members after a starting point to be
selected at random.
c. Stratified Random Sample-strategy for
selecting samples in such a way that
specific sub-groups (strata) will havesufficient number of representative within
the sample to provide ample numbers of
sub-analysis of the members of these sub-
groups.
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d. Cluster Sampling-results when population
is divided into group or cluster. A cluster
sampling technique, is a sampling
technique where groups and cluster not
individuals are selected. It is used when
large-scale survey is undertaken whileother sampling techniques are concerned
only with a few subjects or a few locations.
e. Multistage Sampling-is rarely used,
because of its complexity of its strategyand also it incurs a lot of effort, time and
expense.
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Nonprobability Sample
Convenience Sampling It is asampling strategy based on the
convenience of the researcher. For
instance if the researcher wants toknow about national reconciliation in
the Filipinos in the Philippines
through telephone interviews, he willhave the chance to interview only
those who have telephone to the bias
against those who have no
telephones. Such sampling is done for
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Purposive or deliberate sampling-if the
researcher is interested in finding out
for example, a particular reaction of
some students on the devaluation ofpeso, instead of asking the opinion of
all students in various colleges or
universities in Metro Manila, he maypurposely ask only the group leaders
of a particular college. This is sampling
with purpose.
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