week 4 sampling process

Question 1

what does Accessible population mean?

Answer 1

The portion of the target population, to
whom the researcher can gain access to.
Represents the target population as
closely as possible

Question 2

2 Key considerations for study sample

Answer 2

Representativeness:
- The extent the sample is similar to the
accessible population.

Sampling bias:
- Systematic over- or under-representation of
some segment of the population in terms of a
characteristic relevant to the research
question.

Non-response bias
Sampling bias resulted when a significant
segment of the accessible population refuse to
participate.
Can be detected by comparing the
characteristics of the recruited subjects and the
non-respondents

Question 3

what is the difference between probability sampling and non probability sampling?

Answer 3

probability sampling:
- random selection
- everyone has an equal chance of being selected.

non probability sampling:
- non random
- no way of estimation of probability of each subject being selected.

Question 4

List 3 types of probability sampling

Answer 4

Probability sampling
 Simple random sampling
 Stratified random sampling
 Systematic sampling

Question 5

Explain simple random sampling

Answer 5

Process of randomly select a sample
from the accessible population
Step 1: Establish a “sampling frame”
The actual list of all the elements in the
accessible population
Step 2: Randomly selected the required
number to the study by
Random table
Lucky draw

Question 6

There is a lot of confusion about random
assignment versus random sampling. Please explain the differences.

Answer 6

Random
assignment is a signature of an experiment
design (RCT). If subjects are not randomly
assigned to intervention groups, then the design
is not a true experiment.
* Random sampling by contrast, refers to a method
of selecting people for a study. Random sampling
is not a signature of an experimental design.
In fact, most RCTs do not involve random
sampling. they use non probability sampling.

Question 7

What is 1 advantage of simple random sampling?

Answer 7

 Advantage
Any difference between sample & population
is only by chance.

Question 8

what are 2 disadvantages of simple random sampling?

Answer 8

Disadvantages
 Time-consuming
 Full list of elements of the population might not
be available

Question 9

explain stratified random sampling

Answer 9

Stratified random sampling
Process of selecting a sample to identify
subgroups in the population that are
represented in the sample.

E.g. a population consisting of all RNs in Singapore could be
divided into
– two strata based on gender: M nurse & F nurse.
– three strata based on education: nurse with diploma, nurse
with bachelor degree, nurse with master or above

Step 2: Randomly selected the desired
number of elements from each strata
Proportionate : the elements from each stratum is
proportional to the size of the strata in the
population.
Disproportionate: the proportion of elements from
each stratum is not equal across the included
strata.

Question 10

what is 1 advantage of stratified sampling?

Answer 10

Advantage
Prevents the possibility that some subgroups of
population are under-represented.

Question 11

what are 2 disadvantages of stratified sampling?

Answer 11

Disadvantage
Require more labor than simple random
sampling.
Impossible if information about stratifying
variables is unavailable

Question 12

Explain systematic sampling

Answer 12

Systematic sampling
A process of selecting every kth case from
some pre-existing list of the accessible
population
Define sampling interval:
the standard distance, in terms of number of
individual in a list, between the selected individual
Number of population / number of desired subjects
Recruit the element at each sampling interval

Question 13

What is 1 advantage of systematic sampling?

Answer 13

Advantage
A convenient and efficient method to achieve
the similar effect of simple random sampling.

Question 14

What is 1 disadvantage of systematic sampling?

Answer 14

Disadvantages
Can only be applied if there is a list for the
accessible population.

Question 15

List 3 non probability sampling methods.

Answer 15

Convenience sampling
Consecutive sampling
Snowball sampling

Question 16

Explain convenience sampling method

Answer 16

convenience sampling
Select the most conveniently available
people as participants.
Examples:
Stopping people in the street for interview
Post up advertisement for subject recruitment

Question 17

Explain consecutive sampling method

Answer 17

Consecutive sampling
Recruit entire accessible population
within a defined period of time.

Question 18

Explain snowball sampling method

Answer 18

Snowball sampling
Relies on early sample subjects to refer other who
meet the study eligibility criteria, to participate in the
study.
Accessible population are those with special traits
who are difficult to identify

Question 19

What are 2 advantages of convenience sampling

Answer 19

Advantages:
Convenient and practical

Question 20

What is 1 disadvantage of convenience sampling?

Answer 20

Disadvantages:
Potential sampling bias due to the possibility of
self-selection by the researcher or the subjects.

Question 21

what are the differences between probability and non probability sampling methods?

Answer 21

Comparison of probability and non-
probability sampling
Probability sampling Non-probability sampling

High likelihood of obtaining
a representative sample
Less likely to subject to
sampling bias
Expensive & demanding

Rarely representative of
the target population
Practical and economy
More likely to subject to
sampling bias