Sampling Flashcards
(17 cards)
How would you take a Simple Random Sample?
- Give each unit in the sampling frame a number from 1-n
- Use a random number generator to select numbers that correspond to units
- Continue until desired sample size is reached ignoring repeats
Advantages and Disadvantages of SRS?
Advantages:
- Minimal bias
- Each sample has an equal chance of being chosen
Disadvantages:
- Need a sampling frame/list of population
- Potentially more time-consuming/expensive
How would you take a Stratified Sample?
- Calculate the number to be sampled for each strata ([Strata total÷Pop. total] × sample size)
- Number units 1-n for first strata
- Choose numbers for desired sample size with a random number generator
- Repeat for each strata
Advantages and Disadvantages of Stratified?
Advantages:
- Ensures different categories are fairly represented
- Minimal bias - uses random
Disadvantages:
- More complex/time-consuming
- Need to know the proportions of the population
How would you take Systematic Sample?
- Calculate regular interval (Pop. size÷sample size)
- Number units 1-n
- Use a random number generator to select a number from 1-n
- Use the regular interval to choose the rest of the sample
- If the number exceeds n, wrap around to the start
Advantages and Disadvantages of Systematic?
Advantages:
- Convenient if population is listed
- Quick to implement and select
Disadvantages:
- Needs a total list of population
- Must take care to avoid bias
- Could be patterns in the data
How would you take a Cluster Sample?
- Split population into clusters
- Number each cluster 1-n
- Use a random number generator to select a sample of clusters
- Choose corresponding clusters
- Number all units in the first clusters from 1-n
- Use a random number generator to select sample
- Repeat for all chosen clusters
Advantages and Disadvantages of Cluster?
Advantages:
- Useful if the population is naturally grouped
- Reduces costs/travel etc.
- More convenient
Disadvantages:
- Clusters chosen may not represent the population
How would you take a Judgement Sample?
- Choose people who will have relevant opinions/are qualified to speak on the matter at the Researchers criteria
Advantages and Disadvantages of Judgement?
Advantages:
- Easy and convenient
- Ensure data collection is targeted
- Find persons of interest
Disadvantages:
- Not random
- Potential for bias
- Relies on the judgement/expertise of individuals
How would you take a Snowball Sample?
- Members of the sample refer further participants
Advantages and Disadvantages of Snowball?
Advantages:
- Ensures samples are relevant
- Find difficult to reach targets
- Helps get a larger sample
Disadvantages:
- Not random
- Potential for bias
- Relies on sample volunteering others
How would you take an Opportunity/Convenience Sample?
- Choose sample based on who is easiest to reach
Advantages and Disadvantages of Opportunity?
Advantages:
- Quick and easy
- Collect lots of data easily
Disadvantages:
- Not random
- High risk of bias
How would you take a Quota Sample?
- Stratified but estimates of proportions not accurately calculated
- Samples chosen by opportunity and not random
Advantages and Disadvantages of Quota?
Advantages:
- Do not need to know full information about the population
- Tries to ensure different categories are considered
Disadvantages:
- Not random
- Potential for bias
What is it called if a random sample allows replacement of units?
Unrestricted
