Sampling Techniques and Bias in Research: A Comprehensive Guide, Exams of Design

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MATH^

3307 Lesson 23

Sampling: Terms: Population^ – each

element^ (or^ person)

from^ the^ set^ of

observations

that^ can^ be^ made Sample^ – a^ subset

of^ the^ population Census^ – systematically

getting^ information

about^ an^ entire

population

Sampling^ – studying

a^ part^ (a^ sample)

in^ order^ to^ gain

information

about^ an^ entire

group Sampling^ Frame

• the^ list^ of^ individuals

from^ which^ a

sample^ is^ actually

selected

Popper^ 18: 1.^ A^ sample^ of

50 was^ selected

by^ randomly drawing^ tickets

from^ a^ hat.

2.^ A^ sample^ of

100 was^ selected

by^ subjects^ filling out^ a^ survey^ on

a^ website^ obtained

from^ a posted^ sign.3. A^ sample^ of^200

was^ obtained

by^ surveying individuals^ in^

one^ classroom

for^ a^ population

of

the^ entire^ university.4. A^ sample^ of^100

selected^ by^ randomly

drawing names^ from^ a

hat^ (women^ had

their^ names entered^ twice,

and^ men^ entered

once).

5.^ The^ population

was^ divided^ into

BA^ and^ BS majors^ and^ random

samples^ were

selected^ from each^ group,^ and

then^ combined.

a.^ Simple^ Random^ Sampleb.^ Probability^ Samplec.^ Convenience^ Sampled.^ Voluntary^ Responsee.^ Stratified^ Sample

Random^ Digits A^ table^ of^ random

digits^ is^ a^ long

string^ of^ the^ digits

0 – 9^ where^ each

entry^ in^ the^ table

is^ equally^ likely

to^ be^ any^ of^ the

10 digits^ and^

the

entries^ are^ independent

of^ each^ other. Example:^ You

have^15 employees

and^ you^ wish

to^ select^5 of^

them^ for

a^ training^ program.

Create^ a^ selection

process^ utilizing

a^ Random^ Digit

Table.^

Assign^ each^ of^ the^15

employees^6 2 ‐digit^ numbers. Andy:^ 00,^ 01,^ 02,^ 03,^ 04,

05 Bobby:^ 06,^ 07,^ 08,^ 09,

10,^11 Cathy:^ 12,^ 13,^ 14,^ 15,^

16,^17 Etc….Any^ unassigned^ numbers

your^ skip. Continue^ until^ you^ have

all^5 selected.

The^ design^ of^

sample^ refers^

to^ the^ method

used^ to^ choose

the^ sample

from^ the^ whole

population.* Voluntary^ response^ and

convenience^

sampling^ are^ examples

of

bad^ sample^ design.The design of^ a^ study^ is^ biased

if^ it^ systematically

favors^ certain

outcomes.Undercoverage occurs

when^ some^ groups

in^ the^ population

are^ left^ out

of^ the^ process

of^ choosing^ the

sample. Nonresponse^

occurs^ when^ an

individual^ chosen

for^ the^ sample

can’t^ be

contacted^ or^ refuses

to^ cooperate.

Things^ to

watch^ out

for^ in^ interviewing

technique: •^ Response^ Bias

• when^ an^ interviewer’s

attitude^ suggests

that^ some

answers^ are^ more

desirable^ than

others^ gives^ the

interviewer^ specific

answers^ more

often

-^ Wording^ of^ Questions

• confusing^ or

misleading^ questions

can

introduce^ strong

bias General^ term^ that^ includes

many^ things:^ wording,

body^ language,^ tone^

of^ voice,^ dress

Specific^ type^ of^ response

bias^ where^ the^ wording

of^ the^ questions^ in^ the

concern

Examples:1.^ Identify

the^ population

and^ the^ sample

then

describe^ the

sampling^

method^ that

was^ used.

To^ conduct^ a^ pre

‐election^ opinion

poll^ on^ a^ proposed

city^ ordinance,

a

random^ sample

of^ telephone^

numbers^ from

the^ city^ phone

book^ were

chosen^ and^ called.

(Assume^ all^ who

were^ called^ answered). Population:^ Residents

of^ the^ city Sample:^ The^ people

contacted Sampling^ Method:

Simple^ Random

Sampling Sampling^ Frame:

Phone^ Book

2.^ Determine

if^ the^ study

is^ an^ experiment

or^ an

observational

study.^ Give

a^ reason^

for^ your^ answer.

a.^ A^ personnel

director^ at^ a^ large

company^ studied

the^ eating^ habits

of

employees^ by

watching^ the^

movements^ of

a^ selected^ group

of

employees^ at^

lunchtime.^ The

purpose^ of^ the

study^ was^ to

determine^ the

proportion^ of

employees^ who

buy^ lunch^ in^ the

cafeteria,^ bring

their^ own^ lunches,

or^ go^ out^ to^ lunch. Observational^ Study:^

the^ researcher^ is^ just^

watching^ people^ in^ their

day‐to‐day^ activities.

There^ is^ no

treatment^ or^ control^ imposed.

3.^ It^ is^ believed

that^ 75%^ of^ all

apartment^ dwellers

in^ a^ large^ city

deadbolt^ their

doors^ in^ addition

to^ locking^ them

as^ an^ added

precaution^ against

burglary.^ Describe

how^ you^ would

select^ an^ SRS^

of

20 apartment

dwellers^ to^ survey

if^ there^ are^50

complexes^ in^

the^ city

and^ each^ complex

has^250 residents.

(Use^ the^ random

digit^ table)

Begin^ by^ selecting^10

out^ of^ the^50 apartment

complexes: Assign^ each^ of^ the^50

complexes^2 2 ‐digit^ numbers:

00 01,^02 03,^04 05,^ ….

98 99

Read^ a^ line^ of^ the^ table

until^ you^ have^ your^ first

10 selections. Assign^ each^ resident^4

3 ‐digit^ numbers:^000

001 002 003,^004

006 007,^ …^996 997

999

The^ first^ two^ apartments

selected^ will^ be^ in^ the

sample.

Bias^ is^ present

in^ each^ of^ the

following^ sample

designs^ in^ the

situations

below.^ In^ each

case,^ describe

the^ type^ of^ bias

involved^ and^

state

whether^ you^ think

the^ sampling^

frequency^ obtained

is^ lower^ or^ higher

than^ the^ actual

population^ parameter. 6.^ A^ political^ pollster

seeks^ information

about^ the^ proportion

of

American^ adults

that^ oppose^ gun

control.^ He^ asks

a^ SRS^ of^1000

American^ adults,

“Do^ you^ agree

or^ disagree^ with

the^ following

statement:^ Americans

should^ preserve

their^ constitutional

right^ to^ keep

and^ bear^ arms.”

A^ total^ of^910

or^ 91%^ agreed.

Popper^ 18:^ (a)^ Response

Bias (b)^ Wording

of^ Questions^ (c)

Sampling^ Bias

Wording^ of^ Questions

(Choice^ B):^ By^ using^ the

phrase^ “preserve^ their

constitutional^ rights”