Lecture 7: Sampling Methods

Question 1

What are the types of sampling?

Answer 1

• Simple Random
• Convenience
• systematic
• cluster
• stratified

Question 2

Benefits and drawbacks of Simple Random Sampling

Answer 2

Benefits:

• Theoretically the ideal method of sampling
• You list each member of the
  population and use random numbers to decide which objects are in the sample.
• Each object is equally likely to be selected so it produces an unbiased sample which we hope is representative.

Drawbacks:
- Difficult and expensive to take a simple random sample when dealing with people.

• Practical when a population is geographically concentrated, and a good sample frame exists.
• A sample frame is a list of all the people and objects in the population of interest.
• More easily implemented for natural and manufacturing populations

Question 3

Benefits and drawbacks of Convenience sampling

Answer 3

Benefits:

• Convenient!
• You ask people nearby or people who walk past at a shopping centre
• Or take the next 20 objects off of the production line

Drawbacks:

• Often biased in some way
• But for a quick and cheap poll it may not really matter
• Can have self-selection bias when people choose to participate because they have an interest in the issue in question

Question 4

Benefits and drawbacks of systematic sampling

Answer 4

Benefits:

• Choose a starting point at random
• Systematically take objects at a certain number a part e.g., Population of thousand, want a sample of 50 so take every 20th object.
• Systematic samples are usually easier to administer than simple-random samples and are usually a good approximation of a random sample

Drawbacks:

• However if there is a pattern in the population, certain types of objects could be chosen more or less often than others.

Question 5

Characteristics, benefits and drawbacks of cluster sampling

Answer 5

Characteristics:

• Population is divided into clusters that are then chosen at random e.g., departments of a business or suburbs within a city.
• Within each cluster, all of the objects are included in the sample.

Benefits:

• Can be more convenient and practical than simple-random sampling.

Drawbacks:

• However, if the clusters are different from each other with regard to the elements we are measuring, it can lead to bias or non-representativeness

Question 6

Characteristics, benefits and drawbacks of Stratified Sampling

Answer 6

Characteristics:

• Seems like cluster sampling but the strata or groups are chosen specifically to represent the different characteristics within the population e.g., ethnicity, location, age or occupation
• Within each group a random sample is taken, sometimes in proportion to the size of the group.

Benefits:

• Stratified sampling can lead to a very good random representative sample

Drawbacks:

• Can be complex to administer, and a sampling firm with considerable information about the population is required

Question 7

What is sampling?

Answer 7

“The (process of) selecting a number of respondents (sample) to represent a population of interest.”

Question 8

Why sampling?

Answer 8

• Cannot access the entire population.
• Not easy to speak to the whole of the population.
• Too expensive to speak with the entire population.
• Do not know what the entire population is.
• Not enough time to speak to the population.