Sampling

Question 1

What is simple random sampling

Answer 1

Where members of the population are selected for the sample without replacement

Question 2

How do you conduct a simple random sample

Answer 2

Assign all members (e.g students) of the population (e.g classroom) with a number from 1 to population size (e.g 30)

Use a random number generator to generate sample size (e.g 10) random numbers between 1 and population size (e.g 30)

Ignore any repeats

Select the members (students) of the population (classroom) who have been assigned these numbers

Question 3

What is an unrestricted random sample

Answer 3

A random sample where members of the population are selected for the sample with replacement

Question 4

How do you conduct a unrestricted random sample

Answer 4

Assign all members (e.g students) of the population (e.g classroom) with a number from 1 to population size (e.g 30)

Use a random number generator to generate sample size (e.g 10) random numbers between 1 and population size (e.g 30)

Do not Ignore any repeats

Select the members (students) of the population (classroom) who have been assigned these numbers

Question 5

Advantages and disadvantages of simple / unrestricted random sample

Answer 5

Advantage: Will always give a random sample
No bias in the sample method

Disadvantage: can take a long time
Can be expensive
Need a list of all members in population

Question 6

What is a systematic sample

Answer 6

When members of the population are selected in regular pattern

Question 7

How to conduct a systematic sample

Answer 7

Assign every member (e.g students) of the population (classroom) a number from 1 to population size (e.g 30)

Generate a random number between 1 and (m)

Select the member (students) of the population (classroom) assigned this number, and every ‘m th’ member (student) after this

Question 8

Advantages and disadvantages of systematic sample

Answer 8

Adv: convenient, cheap, easy
You may not need a list of all population

Disadv: not a random sample
May not be representative of the population

Question 9

What is a proportional stratified sample

Answer 9

If the population is divided into different strata, then the proportion of each stratum is fairly represented in your sample

Question 10

How to conduct a proportional stratified sample

Answer 10

Assign each member (student) of the stratum (classroom) a number from 1 to stratum size

Generate (number in stratum to be sampled) random numbers between 1 and (stratum size), ignoring repeats

Select the members (students) of the stratum assigned by those numbers

Question 11

What is a disproportional stratified sample

Answer 11

If the population is divided into different strata and if the proportions in your ample are not representative of the population

Question 12

How to conduct a disproportional stratified sample

Answer 12

Assign each member (student) of the stratum (classroom) a number from 1 to stratum size

Generate (number in stratum to be sampled) random numbers between 1 and (stratum size), ignoring repeats

Select the members (students) of the stratum assigned by those numbers

Question 13

Advantages and disadvantages of proportional stratified sample

Answer 13

Adv: Strata is fairly represented in the sample
Unbiased within the strata

Disadv: you need info about the population
Time consuming and potentially difficult

Question 14

Advantages and disadvantages of disproportional stratified sample

Answer 14

Adv: unbiased within the strata
Each strata is represented in the sample

Disadvantage: strata is not fairly represented in the sample
Need a list of all members in each strata

Question 15

What is a cluster sample

Answer 15

A random sample taken not from the whole population but from selected groups from your population

Question 16

How to conduct a cluster sample

Answer 16

Cluster by ( what the cluster are in context)

Choose (n) (members (students) ) from (m) (cluster (classroom) )

Pick (cluster)

Within each (cluster)
Assign all (members (students) ) of the cluster (classroom) a number between 1 and cluster size

Generate (n) random numbers between 1 and (cluster size)
Ignore any repeats

Select the (members (student) ) of the cluster assigned those number

Repeat for each cluster

Question 17

Advantages and disadvantages of cluster sample

Answer 17

Adv: more convenient than using the whole population
Don’t need a list of the entire population, just for individual cluster

Disadv: the cluster chosen may not be representative of the population
There may be less variation within each cluster

Question 18

What is judgmental sample

Answer 18

When members of the population are selected according to criteria based on the judgment of the sample

Question 19

How to conduct a judgmental sample

Answer 19

Identify the member (students) of the population (classroom) most useful to the investigation

Pick them

Question 20

Advantages and disadvantages of judgmental sampling

Answer 20

Adv: east, cheap quick to carry out

Disadv: totally non random
Biased towards judgment of the data collector

Question 21

What is a snowball effect sample

Answer 21

When members of the same recommended or refer new members into the sample

Question 22

How to conduct a snowball sample

Answer 22

Choose as many members (students) of the population (classroom) that will be useful

Use these members (students) to identify further members of the population that will be useful

Select these members (students friends)

Repeat

Stop (at some time)

Question 23

Advantages and disadvantages of snowball sample

Answer 23

Adv: easy cheap and quick
High yield of results for minimal effort

Disadvantage: totally non random
Mostly self selecting