•In conducting a study, the researcher
may study every member of a given
population or just representative
sample of that population.
• For various reasons, a study of a
sample of the population is often done
instead of complete enumeration.
•The process of choosing a
representative sample of population is
Selecting the Study Population
•The information collected in order to answer the
objectives of a study is obtained from
EXAMPLE. In the study of Attitudes of Farmers and
Landowners towards Land Reform. The attitudes
that will be examined are those of farmers and
landowners, and they will most likely be the
source of information. These cases or individuals
are commonly called research subjects or
•Once the type of cases to be studied has been
determined, the researcher must decide next how
the cases will be selected. For this purpose, it is
important to distinguish between the total
population and the sample from which the data will
•The population is composed of elements, each of
which is a potential case in study. Depending on
the objectives of the study , the available resources
and the available time for the study, a researcher
may decide whether to study all the available
elements or cases in a population or just a sample
from the entire population. The usual practice is to
select and study a small sample of the total
population. This process is called sampling.
The Nature of Sampling (Fraenkel and Wallen, 1996)
•Sampling is the process of choosing a representative
portion of a population or some elements in a population
that will represent the entire population.
•It is assumed that the characteristics of the chosen
elements, called sample, reflect the characteristics of
the entire population. In contrast total enumeration or
census requires the study of all elements in the
In the study of sampling, it is important to distinguish the
following concepts: population, target population,
sampling population, sampling frame and sample.
1. Population refers to the total number of elements
(e.g. items, objects, areas, or individuals) to be
For example, in the study of Sexual Attitudes and
Practices of Students in Public High Schools in
Province A, all students in public high school in the
province constitute the study of population.
1. Target Population is the population for which
representative information is desired.
2. Sampling Population is the population from which a
sample is actually drawn.
3. Sampling Frame is the list of all elements or
sampling units (e.g. items, persons) in a population.
The sample is drawn from the sampling frame.
4. Population Elements pertains to an item, an object,
an area, or an individual on which data will be taken.
It is considered the unit of study. In the example
above, a student in a public high school is a
5. Sample refers to an individual, an element or a
group of individuals or elements on which information
is obtained. The sample is drawn from a population to
which research results are generalized.
Why Study a Sample?
There are several advantages of studying a sample
rather than the total population. Studying a sample is generally
cheaper, faster, and yields more accurate results than
conducting total enumeration.
It is cheaper. Since a sample is smaller than the entire
population, collection and processing of data, therefore,
costs much less.
It is faster. It is definitely quicker to study fewer individuals or
elements than an entire population.
It is more accurate. Fewer errors are expected in data
collection and processing in a study of a sample than in a
study of the entire population.
It ca yield more comprehensive information. A small
sample can be more thoroughly investigated and can yield
more comprehensive information than a big population.
Basic Types of Sampling
Non-probality Sampling. It is arbitrary (non-
random) and is generally subjective. Data
gatherers choose sample cases, “as they wish”
or “wherever they find them.”
Probality Sampling. It is based on the concept
of random selection, a procedure that assures
that all elements in the population are given an
equal chance of being selected as a sample