Data Collection

Question 1

What is a population?

Answer 1

• A collection of the whole of something
• All elements sharing some set of characteristics;
• If we have a population we can get parameters - true values
• Census
  
  • A study of all elements of a population

Question 2

What is a sample?

Answer 2

• A set of individuals drawn from a population
• If we have a sample we can get statistics - values that estimate the parameter
• Sample characteristics = statistics
• Needs to be representative of full population

Question 3

What kinds of error are there?

Answer 3

• Sampling error

* Non-sampling errors

Question 4

What is sampling error?

Answer 4

• The difference that exists between a population and a sample as a result of the sample selection.
• Will be reduced by taking a larger sample

Question 5

Why are non-sampling errors a problem and what kinds are there?

Answer 5

• Larger samples won’t reduce non sampling errors so more serious
• Coverage error
• Nonresponse error
• Measurement Error

Question 6

What is coverage error and how is it reduced?

Answer 6

• Results from selection bias
• No matter what, some people will never be in sample
• Reduced by having an adequate sampling frame (up to date list of all items from which you will select the sample)

Question 7

What is non-response error?

Answer 7

• Some people will never choose to do surveys
• Upper and lower economic classes have differing survey response frequency
• Can’t assume that people who do respond to surveys are the same as those who don’t

Question 8

What is measurement error?

Answer 8

• Ambiguous wording of questions
• Hawthorne effect
  
  • Respondent feels obliged to please the interviewer
• Respondent error

Question 9

What are the steps to taking a sample?

Answer 9

• Define the sample frame
• Choose nonprobabliity or probability sampling
• Chose a sampling plan

Question 10

What is a sample frame?

Answer 10

• A list of all the items that make up the population
• Choice of frame important
• Sample is then chosen from the sample frame

Question 11

What is the difference between probability and non-probabilty sampling?

Answer 11

• Non probability sampling
  
  • Choose the items to be included without knowing their
    probabilities of selection
  • Cannot apply stasitical inferences
  • Cheap and dirty
• Probability sampling
  
  • Select items based on known probabilities
  • Statistical inferences allowed

Question 12

What are the non-probability sampling plans?

Answer 12

• Convenience
• Judgemental
• Quota
• Snowball

Question 13

What are the probability sampling plans?

Answer 13

• Simple random
• Systematic
• Stratified
• Cluster

Question 14

What is cluster sampling?

Answer 14

• Divides the population into clusters, a number of clusters is selected to represent the population and all units within selected clusters are included in the sample
• Cheap, easy, reduced field work
• Imprecise, difficult to compute and interpret results
• Properties, households, homes

Question 15

What is stratified sampling?

Answer 15

• The population is divided into groups called strata from which a simple random sample is drawn
• Objective is to form strata such that the population values of interest within each stratum are as much alike as possible
• Includes all important sub-populations, precision
• Difficult to select relevant stratification variables, not feasible to stratify on many variables

Question 16

What is systematic sampling?

Answer 16

• The population is arranged and there is an interval between each selection (production line)
• Can increase representativeness, sampling frame not necessary
• Can decrease representativeness

Question 17

What is simple random sampling?

Answer 17

• Each item in a population has an equal chance of inclusion
• Simple & easy for small populations
• Difficult to construct sampling frame, expensive, lower precision

Question 18

What is snowball sampling?

Answer 18

• Existing study subjects recruit additional ones
• Can estimate rare characteristics
• Time consuming

Question 19

What is quota sampling?

Answer 19

• Population is segmented into subgroups, then judgement is used to select units from each segment based on a specific proportion
• Samples can be controlled for certain characteristics
• Selection bias, no assurance of representativeness

Question 20

What is judgemental sampling?

Answer 20

• Researcher chooses samples based on their view of who would be helpful for the study
• Low cost & time
• Does not allow generalisation, subjective

Question 21

What is convenience sampling?

Answer 21

• Members of the population are selected by the ease of access to them
• Least cost & time
• Selection bias, sample not representative