Chapter 1 - Data Collection Flashcards
What is a Population?
✯ The whole set of items that are of interest.
What is a Sample?
✯ A selection of observations taken from a subset of the population used to find out information about the population as a whole.
What is a Census?
✯ Observes or measures every member of the population.
What is a Sampling Unit?
✯ Individual units of a population.
What is a Sampling Frame?
✯ Sampling units can be individually numbered or named to form a list called the sampling frame.
e.g. the register of people attending a school.
What happens to the accuracy as the sample size increases?
✯ As sample size increases ↑, the accuracy of the result also increases ↑.
Provide an advantage of using a census.
✯ Gives a completely accurate result.
Give me at least two advantages of using a sample.
✯ Quicker & Cheaper
✯ Easier
✯ Less data to process
Give me at least two disadvantages of using a census.
✯ Time consuming and expensive
✯ Cannot be used in destructive tests.
✯ Lots of data to process.
Give me two disadvantages of using a sample.
✯ Data may not be accurate
✯ Sample may not be large enough to represent small groups.
How do we carry out a simple random sampling method?
- Assign a # to units.
- Then use a random # generator to obtain a set of unique numbers.
- Go back to the original population and select people corresponding to these numbers.
Name at least two advantages of simple random sampling.
✯ Bias free
✯ Easy & Cheap
✯ Each unit has an equal and known chance of being selected.
Name at least two disadvantages of simple random sampling.
✯ Not suitable with large sample sizes.
✯ Sampling Frame needed
How do we carry out systematic sampling?
- Find K = Population Size/ Sample Size
- 1st person is chosen at random.
- Every regular interval (Every kth item) select a person until the sample size desired has been reached.
Name at least two advantages of systematic sampling.
✯ Simple and Quick
✯ Suitable for large populations.
Name at least two disadvantages of systematic sampling.
✯ Sampling Frame is needed.
✯ Can introduce bias if sampling frame is not random.
How do we carry out stratified sampling?
- Divide sample into strata
- Use formula to calculate proportions of each member in each strata.
Number in stratum/ Number in population x Overall Sample Size
- Then follow the same steps as simple random sampling…
What are two advantages of stratified sampling?
✯ Reflects population structure.
✯ Guarantees proportional representation of strata.
What are two disadvantages of stratified sampling?
✯ Population must be clearly classified.
✯ Selection within strata suffers from the same disadvantages as simple random sampling.
What is opportunity sampling?
✯ Units are found at the same time the survey is being carried out
Name me at least one advantage of opportunity sampling.
✯ Easiest to carry out
✯ Inexpensive.
Name me at least one disadvantage of opportunity sampling.
✯ Highly unlikely to provide representative sample.
✯ Highly dependent on interviewer.
What is quota sampling?
✯ Population is already divided into groups.
✯ A quota is set for each group e.g. We want 20 people who are year 11s.
✯ The interviewer then selects sampling units that fit the quota.
Name me at least two advantages of quota sampling.
✯ Allows small sample sizes to be representative.
✯ No sampling Frame needed
✯ Comparison between groups.
What is the difference between stratified sampling and quota sampling?
✯ Quota sampling is different from stratified sampling as it may not be proportional to how many in each group actually exist and a sampling frame is not needed
whereas…
✯ in stratified sampling the exact proportions of the population is needed, and a sampling frame is required.
Name me at least two disadvantages of quota sampling.
✯ Non-random sampling can introduce bias.
✯ Population must be already divided into groups: it could be costly or inaccurate.
✯ Non-response not recorded.
What is qualitative data?
✯ Non numerical values.
What is quantitative data?
✯ Numerical values.
What is discrete data?
✯ A range of specific values
What is continuous data?
✯ Any decimal value.
What are class boundaries?
✯ Maximum and minimum values that belong in each class.
What is the midpoint?
✯ The average of the class boundaries.
What is the class width?
✯ Difference between upper class and lower-class boundaries.
What is a modal class?
✯ Highest frequency class.
