Sampling Flashcards
What is a population?
The whole set of/all items that are of interest
What is a census?
An observation of all/every member of the population
2
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
1
List the advantages of a census
- Should give completely accurate result
4
List the disadvantages of a census
- Time consuming and expensive
- Cannot be used when testing process destroys the item
- Hard to process large quantities of data
- Hard to get everyone to respond
- Less time consuming and expensive than a census
- Fewer people have to respond
- Less data to process than in a census
3
List the disadvantages of a sample
- Data may not be as accurate
- Sample may not be large enough to give information about small sub-groups of the population
- Possible bias
What is a sampling frame?
An ordered list of the sampling units of the population
What are sampling unit?
Individual units of a population
What is a common way to improve a sample?
Test a larger number of (avacados)
1
What do all random sampling methods require
A sampling frame
What is simple random sampling?
sampling where every sample of size n has an equal and known chance of selection
2
What are techniques for simple random sampling?
- Generate a number: random number generator, random number table
- Lottery sampling: tickets picked from a hat
What is systematic sampling?
Sampling where the required elements are chosen at regular intervals from an ordered list
2
What is stratisfied sampling?
- Population is divided into mutually exclusive strata/groups (e.g. males and females)
- A random sample is taken from each
3
List the advantages of simple random sampling
- Free of bias
- Easy and cheap to implement for small populations and small samples
- Each sampling unit has a known and equal chance of selection
2
List the disadvantages of simple random sampling
- Not suitable when the population or sample size is large
- A sampling frame is needed
2
List advantages of systematic sampling
- Simple and quick to use
- Suitable for large samples and large populations
2
List disadvantages of systematic sampling
- A sampling frame is needed
- It can introduce bias if the sampling frame is not random
2
List advantages of stratisfied sampling
- Sample accurately reflects population structure
- Guarantees PR of groups within population
2
List disadvantages of stratisfied sampling
- Population must be clearly classified into distinct strata
- Selection within each stratum suffers from the same disadvantages as simple random sampling
3
List common general errors in sampling
- Error in sampling frame
- Some data is erroneous
- Natural variance (due to small sample or different samples lead to different results)
What is quota sampling?
An interviewer/researcher selects a sample that reflects the characteristics of the population as a whole (interviewer selects actual sampling)
2
What should be done once quota sampling has begun
- Continue collecting data/info until all quotas are full
- If quota full, further responses should be ignored
2
What is opportunity sampling?
Taking sample from people who:
1. are available at the time of the study
2. who fit the criteria you are looking for (eg. elderly people)
4
List the advantages of quota sampling
- Allows a small sample to be representative of the population
- No sampling frame required (interviewer selects sample)
- Quick, easy and inexpensive
- Allows for easy comparison between different groups within a population
4
List the disadvantages of quota sampling
- Non-random sampling can introduce bias
- Population must be divided into groups which can be costly or innacurate
- Increasing scope of study increases number of groups, which adds time and expense
- Non-responses are recorded as such
2
List the advantages of opportunity sampling
- Easy to carry out
- Inexpensive
2
List the disadvantages of opportunity sampling
- Unlikely to produce representative sample
- Highly dependent on individual researcher (bias)
Variables associated with numerical observations are called (…) data/variables
quantitative
Variables associated with non-numberical observations are called (…) data/variables
qualitative
A variable that can take any value in a given range is a (…) variable
continuous
A variable that can take only specific values in a given range is a (…) variable
discrete
