Population the entire set of individuals or objects
having some common characteristics selected for a
research study. E.g. patients admitted to intensive
Sample may be defined as representative unit of a
target population, which is to be worked upon by the
researchers during their study.
“A population is a complete set of persons or objects
that possess some common characteristics that is of
interest to the researcher.”
The population for a study usually is described as
being composed of two groups-
The target population which is also called the
universe is composed of the entire group of people
or objects to which the researcher wishes to
generalize the findings of the study.
The target population consists of people or things
that meet the designated set of criteria of interest to
A researcher is interested in identifying the
complication of DM typeII among people who have
migrated to Ludhiana.
In this instance, the target populations are all the
migrants at Ludhiana suffering with DM typeII.
It is aggregate of cases that confirm to designated
criteria and are also accessible as subjects for study.
By identifying the group from which the study
sample was chosen, the investigator about the
conclusion of the generalizability of research
A research is conducted on the registered nurses
(RN) working in Dayanand Medical College and
Hospital (DMCH), Ludhiana.
In this case the population for this study is all RNs
working in DMCH, but some some of them may be
on leave and may not be accessible for research
study. Therefore accessible population for this study
will be RNs who meet the designated criteria and
who are also available for the research study.
The criteria that specified the characteristics that people in the
population must possess are sometimes referred as Eligibility Criteria
or Inclusion Criteria.
To be eligible for a study on myocardial infection, the patient must be:
Hospitalized because of MI or coronary angiography.
1. Have no prior history of CAD.
2. Be older than 18 years of age.
3. Be in haemodynamically stable condition and free of pain for 24 hours.
4. Be oriented to person, place and time.
5. Able to speak or understand English.
6. The people may be defined to exclude who does not speak English.
Inclusion and Exclusion criteria for a study often reflects considerations
other than a substantive or theoretical interest in certain types of people.
The criteria for defining the population may reflect one or more of the
1. COSTS: some criteria reflects costs constraints. For example, when a non-
English speaker people are excluded. This does not necessarily mean that
the researcher is not interested in English speakers , but may rather reflect
the fact that the researcher cannot afford to have translators.
2. PRACTICAL CONCERNS: There are other practical concerns such as
difficulty in including people in rural areas, people with hearing
3. PEOPLE ABILITY TO PARTICIPATE IN A STUDY: The health condition of
some people may preclude their participation. Example, people with
mental impairments, who are in coma.
4. DESIGN CONSIDERATIONS: it is sometimes advantageous to define a
fairly homogeneous sample as means of controlling extraneous variables.
Sample may be defined as representative unit of target
population which is to be worked upon by researchers during
Quantitative researchers often select samples that will allow
them to achieve stating conclusion validity and generalize
their result. They therefore develop a sampling plan that
specifies in advance how study participants are to selected
and how many to include.
Qualitative researchers make sampling decision during the
course of data collection based on information & theoretical
need & typically do not develop a formal sampling plan in