Evidence-Based Practice for Nurses

Type of

Sampling Assumptions

Possibility

of Bias Representativeness

Other

Comments

Simple

random

sampling

Each subject has

the same chance

to be selected

Strategy used to

select subjects

upholds

randomization

Low risk of bias

if randomization

of subjects is

upheld

With each subject

having the same

chance for selection,

high probability the

sample will represent

the population as

long as sample size is

sufficient

Time

consuming for

researcher if

the study has

a large sample

size

Stratified

random

sampling

Strata must be

mutually exclusive

so a subject can

be assigned to

only one stratum

Random

sampling used

to select subject

from each

stratum

Low risk of bias

if randomization

of subjects is

upheld

If assumptions

are upheld, high

probability the

sample will represent

the population if the

number of subjects

in each stratum is

sufficient

Time

consuming for

researcher if

the study has

a large sample

size

Cluster

sampling

Simple random

sampling used

to first select

groups or clusters

and then select

subjects within

each cluster

Potential for

bias greater

if the initial

clusters selected

under- or

overrepresent

groups within

the population

Greater potential

for the sample

to not represent

the population

depending on how

the initial clusters are

selected

Less time

consuming than

the first two

because the

initial clusters

focus the sites

for subject

selection

Systematic

sampling

Begin sampling

with a random

start. Start

counting each kth

subject on the list

by first identifying

the start location.

Or, close eyes and

point to a number

on the list to start

the counting

Some bias may

be introduced if

randomization

of start

location is not

maintained

If bias occurs, not

as representative of

population as other

three sampling

methods

Simpler to

complete

than the other

three forms

of probability

sampling

Data from Gray, J., Grove, S., & Sutherland, S. (2016). Burns and Grove’s the practice of nursing

research: Appraisal, synthesis, and generation of evidence (8th ed.). St. Louis, MO: Saunders;

Polit, D., & Beck, C. T. (2014). Essentials of nursing research: Appraising evidence for nursing

practice. Philadelphia, PA: Lippincott Williams & Wilkins.

TABLE 11-1 Overview of Probability Sampling Methods

11.2 Sampling Methods 291