Sampling

Question 1

What are the steps of simple random sampling?

Answer 1

-Assign each member a number from 1 to n (using a sampling frame)

-Then using a random number generator, pick unique numbers until sample is fulfilled

Question 2

What are the advantages and disadvantages of simple random sampling?

Answer 2

Advantages:
-Easy and cheap for small samples and populations
-No bias

Disadvantages:
-Not suitable for large populations
-Sampling frame is needed

Question 3

What are the steps for systematic sampling?

Answer 3

E.g for a sample of 100 in a population of 20000:

-Using a sampling frame, assign each member a number from 1 to 20000

• (20000/100 =200)
  -Using a random number generator create a number from 1-200

-Then starting with that unit, select every 200th unit until there’s a sample of 100

Question 4

What are the advantages and disadvantages of systematic sampling?

Answer 4

Advantages:

-Suitable for large populations

Disadvantages:

-May be biased and can introduce a pattern

Question 5

What are the steps in stratified sampling?

Answer 5

E.g for a sample of 30 where there’s 45 girls and 105 boys:

45+105=150
(45/150) x 30 = 9 girls needed for sample
(105/150) x 30= 21 boys needed for sample

-Assign each girl a number from 1-45
-Then using a random number generator, select 9 unique numbers

-Assign each boy a number from 1-105
-Then using a random number generator select 21 unique numbers

Pick each boy and girl corresponding to their number

Question 6

What are the advantages and disadvantages of stratified sampling?

Answer 6

Advantages:

-Proportional representation of population

Disadvantages:

-Sampling frame is needed

Question 7

What is quota sampling like?

Answer 7

Like stratified sampling, but it’s a quota that has to be filled before the sample is completed

Members are picked non randomly (may be biased)

Question 8

What are the advantages and disadvantages of quota sampling?

Answer 8

Advantages:

-No sampling frame needed
-Cheap

Disadvantages:

-Can introduce bias
-Depends on knowledge and expertise of researcher

Question 9

What is opportunity sampling?

Answer 9

Where the researcher tries to gain data as quickly as possible (by researching on the first people available) in order to fill sample ASAP

Question 10

What are the advantages and disadvantages of opportunity sampling?

Answer 10

Advantages:

-Easy to carry out
-Cheap

Disadvantages:

-Can be biased as it may not be random as to who is picked by the researcher