Sampling Flashcards
Census
- Observes or measures every member of a population.
Sample
- Selection of observations taken from a subset of the population which is used to find out information about the population as a whole.
Advantage of Census
- Gives a completely accurate result.
Disadvantages of Census
- Time Consuming
- Expensive
- Can’t be used when testing process destroys the item.
Advantages of Sample
- Less time consuming and expensive than a census.
- Fewer people have to respond.
- Less data to process than in a census.
Disadvantages of Sample
- Data may not be as accurate.
- Sample may not be large enough to give information about small sub-groups of the population.
Simple Random Sample
- Every sample of size has an equal chance of being a selected.
How Carry Out Simple Sample?
- Sampling frame, each person in SF allocated a unique number and they’re chosen at random.
Systematic Sampling
- Required elements are chosen at regular intervals from an ordered list.
- Take every fifth person from a sample.
Stratified Sampling
- Population is divided into mutually exclusive strata and a random sample is taken from each.
Advantages of Simple Random Sampling
- Free of Bias
- Easy and cheap to implement for small populations/samples.
- Each sampling unit has a known and equal chance of selection.
Disadvantages of Simple Random Sampling
- Not suitable when the population size or the sample size is large as it is potentially time consuming and expensive.
- Sampling frame is needed (Electoral Roll).
Advantages of Systematic Sampling
- Simple and quick to use.
- Suitable for large sample and populations.
Disadvantages of Systematic Sampling
- Sampling frame is needed.
- Can introduce bias if the sampling frame is not random.
Advantages of Stratified Sampling
- Sample accurately reflects the population structure.
- Guarantees proportional representation of groups within a population.
Disadvantages of Stratified Sampling
- Population must be clearly classified into distinct strata.
- Selection within each stratum suffers same Ds as SRS; not suitable when large populations/samples.
Quota Sampling
- An interviewer selects a sample that reflects the characteristics of the whole population.
- Divided into groups according to characteristics.
- Meet people, allocate them to the appropriate quota until its fulfilled.
Opportunity Sampling
- Consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.
- Pick the first 20 people you see.
Advantages of Quota Sampling
- Allows a small sample to still be representative of the population.
- No sample frame required.
- Quick, easy and inexpensive.
- Allows for easy comparison between different groups within a population.
Disadvantages of Quota Sampling
- NRS can introduce bias.
- Population must be divided into groups, costly or inaccurate.
- Increasing scope of study increases number of groups, adds time and expensive.
- Non responses are not recorded.
Advantages of Opportunity Sampling
- Easy to carry out
- Inexpensive.
Disadvantages of Opportunity Sampling
- Unlikely to provide a representative sample.
- Highly dependent on individual researcher.
