• Definition of Variable
• Definition of population
• What is sample?
• Sample and population
• What is sampling and sampling methods
• Instrument and instrumentation
Understanding of variables
• A variable is a measurable characteristic
• A variable is any characteristic or quality
that varies among the members of a
Understanding of variables
A variable is a concept-a noun that stands
for variation within a class of object, such
• marital status
• Number of children
Dependent and Independent
• An independent variable is a variable
presumed to affect or influence other
• A dependent variable (or outcome) is a
variable presumed to be affected by one
or more independent variables.
Definition of Population
A population is the group to which the
results are intended to apply.
The term “population” is as used in
research, refers to all the members of a
It is the group of interest to the researcher,
the group to whom the researcher would
like to generalize the results of a study.
Examples of Population
• All high 10th-grade students in the united sates
• All elementary school gifted children in the state of
• All first-grade physically disabled students in Omaha
who have participated in preschool training
• First, population may be virtually any size and may
cover almost any geographical area.
• Second, the entire the researcher really would like to
generalize is rarely available
Sample and Population
• A sample is a group in research study on which
information is obtained.
• The sample is smaller than the population.
• The small group that is observed is called a sample,
and the larger group about which the generalization is
made is called a population
• A population is defined as all members of any well-
defined class of people, events or objects. A sample is
a portion of a population.
Steps in Sampling
The population that the researcher would like to generalize
to is referred to as the target population
Since it is usually not possible to deal with the whole of the
target population, one must identify the portion of the
population to which one can have access-called the
From the accessible population, one selects a sample in
such a way that it is representative of the population.
All fifth-year students enrolled in teaching training
programs in the United States.
All fifth-year students enrolled in teaching-training
programs in the state university of New York.
Two hundred fifth-year students selected from
those enrolled in the teacher training programs
in the State university of New York.
There are two methods are commonly
known in social science research. These
1. Random Sampling
2. Non-random sampling
Random sample is one in which each and
every member of the population has an
equal and independent change of being
• The population is all 300 eight-grade
students enrolled in general math at
central Middle school.
Type of Random Sampling
The four types of random sampling most
frequently used .These are:
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Systematic sampling
The major forms of non-random sampling
• Purposive sampling
• Convenience sampling
Type of Non-random Sampling
• Purposive sampling is referred to as judgment sampling.
• Sample elements are judged typically or chosen from the population.
Purposive sampling is a selective sampling because the individual or
respondent has special qualification.
• Much of the sampling in qualitative research is purposive. Purposive
sampling is appropriate in three situations.
• First, If a researcher wants to use content analysis to find cultural
themes. In that case, the researcher needs to select a community.
• Second, a researcher may use purposive sampling if he or she
wants investigate for a special group. If the researcher wants to
conduct research, he or she needs to be selective. It is impossible
to list all prostitute and sample randomly from the list..
• Third, a researcher may use purposive sampling when he or she
wants to identify particular types of cases for in-depth investigation.
Non-random Sampling (cont’d)
Instrument and Instrumentation
• Any device/material that the researcher uses to
collect data throughout the research is called
• The device the researcher uses to collect data is
called an instrument.
• The device can be a pencil and paper test,
interview, a questionnaire, or a rating scale.
• The whole process of collecting data is called
Data Analysis (Qualitative)
Instruments for qualitative study are :
Qualitative Data Analysis
The transcribed interviews with the field notes will be
examined and classified into the themes.
The tape-recorded interviews were fully transcribed and
great care was taken to protect the secrecy of
The researcher followed the same sequence for the
observation. When staying in the field, the researcher
quickly write down the notes. To gathering information
depends on the researcher’s understanding of the
research problem and the subject under the study.
Quantitative Data Analysis
Instrument for Quantitative data are :
• a questionnaire
• or a rating scale
• Software (SPSS)
Quantitative Data Analysis (Cont…)
Quantitative data can be analyzed using the
Statistical Package for the Social Science
The questions can be coded before being
entered into the computer to be analyzed.
For the simple descriptive study frequencies,
standard deviation, mean and percentages,
minimum and maximum value can be largely
used for research .