Kinds of Sampling
Lesson 3
Sampling Designs
•Probability Sampling
The Sample size (n)
These sampling techniques make use of the “chance
process” in selecting the sample of the study.
Sloven’s Formula:
•Non-probability Sampling
n =
These sampling techniques do not make use of the
“chance process” in selecting the sample of the
study.
N
1  Ne 2
Probability Sampling
N = is the population size
e = is the margin of error usually
0.01 or 0.05
•Random Sampling
•Systematic Sampling
•Cluster Sampling
•Stratified Random Sampling
1,000 pupils from an elementary
school in Sampaloc District
0.05 margin of error
Random Sampling
Every member of the population is given an equal
chance of being selected.
where:
Example:
If: N =
e =
1,000
sample size (n) =
1 + 1,000 (0.05)2
n =
n =
1,000
3.5
285.7  286 pupils
Sampling Technique
The process of selecting a representative of the
population in which everyone in the population is
given a chance to become a member of the sample.
1. Sampling error
May be committed in the actual choosing of the
sample
Example:
Small size of the sample
2. Non-sampling error
May be committed due to outside factors not related
to sampling. It includes all kinds of “human errors”
Example:
Malfunctions of the instruments used in
measurements and computation
The simplest (basic) method of random sampling is
by LOTTERY
Systematic Sampling
•If the objects or individuals are arranged in some
ways such as alphabetical or numerical, a random
starting point can be selected and then every kth
element encountered thereafter becomes a sample.
•When the bottom of the list is reached, the
counting is continued at the top.
Example:
The list of 550 Nurse board passers is numbered in
order and they are to be used in a study:
The steps in systematic sampling process are a
follows:
1. Compute n using Sloven’s formula
( use e = 0.05)
n =
N
1  Ne 2
n
=
550
1  5500.05
2
= 232 board passers
2. The kth interval will be found by the formula
k = N / n.
k
= N = 550
n
232
=
The distribution of students from each city was
known and shown in Table 1.
Determine n and the number of proportional
sample for each of the four cities.
2.37  2
Table 1
The Number of Students Who Took the NSAT in
the Four Cities in Metro Manila
3. A random number is to be selected from the
random number table or the calculator.
If the random number 25 is selected, whoever is
board passer number 25 is the 1st sample and from
number 25 to 550 every 2nd name will be taken as a
sample.
Cluster Sampling
This is sometimes referred to as “area sampling”
because the population is spread out over a wide
area.
Here the population is subdivided into groups
(clusters).
Example:
Suppose the Dean of Student Affairs of UE wants to
know the perception of members of the different
student organizations about a certain school
regulation.
Caloocan City
N =
Step 1 : Compute the percentage
Table 2
The Number of Students Who Took the NSAT in
the Four Cities in Metro Manila
Population
Size
150,000
120,000
40,000
90,000
400,000
CITY
Manila
Quezon City
Pasay City
Caloocan City
N =
He can use a cluster sample by interviewing some
or all of the members of selected student
organization.
For each of these strata, the sample size will be
drawn proportionately.
Decimal
Percent
0.375
0.3
0.1
0.225
Sample computation:
Decimal % =
Stratified Random Sampling
This is used for research work of population which
is composed of several categories or strata.
Population
Size
150,000
120,000
40,000
90,000
400,000
CITY
Manila
Quezon City
Pasay City
150,000 = 0.375
400,000
Step 2. Compute n .
N =
e =
400,000 high students
0.01 margin of error
N
Random sampling may be applied to each stratum
to choose the individual sample for the study.
Example:
A study is conducted to 400,000 high school seniors
who took the NSAT in the four (4) cities of Metro
Manila namely: Caloocan City, Manila, Pasay City,
and Quezon City.
sample size (n) =
1 + Ne2
400,000
n
=
1 + 400,00 (0.01)2
n
=
9,756 students
Step 3 : Compute sample size for the four cities.
Table 3
The Number of Students Who Took the NSAT in
the Four Cities in Metro Manila
CITY
Manila
Quezon City
Pasay City
Caloocan City
N =
Population Size
150,000
120,000
40,000
90,000
400,000
Non - Probability Sampling
Decimal Percent
0.375
0.300
0.100
0.225
Sample Size
(9,756) (0.375) = 3,658
(9,756) (0.300) = 2,927
(9,756) (0.100) = 976
(9,756) ( 0.225) = 2,195
n = 9756
3. Quota Sampling
Selection is done according to pre-determined
quotas.
•Convenience Sampling
•Purposive Sampling
•Quota Sampling
Each person gathering observations is given a
specified number of elements to sample.
1. Convenience Sampling
Available individuals are used in the study.
The decision as to whom to interview is usually left
to the discretion of the interviewer.
Example:
A teacher who will use one section under her
tutelage as the object of her study.
2. Purposive Sampling
Deliberate selection of individuals is done for the
study. The researcher is allowed to use his own
discretion as to which individuals will fit the
requirements or the purpose of the study.
Example:
Consider the research on “The Lifestyle of Filipino
Women Married to Asian Men”.
Only Filipino women who are married to men from
Japan, Thailand, Vietnam, etc. can be considered as
sample to this study.
References:
Basic Statistics
Raymond Ang, Lota Billones, Wilma Dechavez, &
Aileen Diansuy
Elementary Statistics: A Modern Approach
Priscilla Altares, Antonio Roland I. Copo, Yonardo
Gabuyo, Angeline T. Laddaran, Leila Mejia,
Immaculata Policarpio, Evangeline Agueda Sy,
Helen Tizon, & Ana Maria Yao
Statistics
Rosita De Guzman Santos, Teofilo de Guzman,
Athena Ungriano, & Erna Yabut
End of Lesson 3
prepared by:
Dr. Leila R. Gano