Data Collection Flashcards
Population
The whole set of items that are of interest
Census
Measures or observes every member of a population
Sample
A selection of observations taken from a subset of population and used to find out more information about the population as a whole
Advantages of a Census
- Results should be completely accurate
Disadvantages of a Census
- Time consuming and expensive
- Cannot be used when testing destroys process
- Hard to process large quantity of data
Advantages of Sample
- Less time consuming and cheaper
- Fewer people have to respond
- Less data needs to be processed
3 types of Random Sampling:
- Simple Random Sampling
- Systematic Sampling
- Stratified Sampling
What are Sampling units?
Individual units of a population that are named and numbered to form sampling frame
Disadvantages of Sample
- Data may not be accurate
- Sample may not be large enough to give information about small subgroups of the population
What is Random Sampling?
- Where each member of the population has an equal chance of being selected
- The sample should be representative of the population and bias should be removed
What is Simple random sampling?
Where every sampling unit in the sampling frame has an equal chance of being selected
How to carry out Simple Random Sampling?
- Allocate a number between 1 and N to each sampling unit, within the sampling frame
- Use a random number generator or method of lottery sampling to select X numbers between 1 and N
- Units corresponding to these numbers become the sample
Advantages of Simple Random Sampling
- Free of Bias
- Easy and cheap for small samples and populations
- Each sampling unit has a known and equal chance of selection
Disadvantages of Simples Random Sampling
- Not suitable for large samples and populations
- Sampling frame is needed
What is Systematic Sampling?
Where required elements are chosen at regular intervals in ordered list
How to carry out a Systematic sample?
- Divide the population size of by the sample size to obtain the interval of k
- Then use a random generator to obtain a unit between 1 and k
- Start with the unit obtained and go up in the interval you worked out
Advantages of Systematic Sampling
- Simple and quick to use
- Suitable for large samples and large populations
Disadvantages of Systematic Sampling
- Bias introduced if sampling frame is not random
- A sampling frame is needed
What is Stratified Sampling?
- Where the population is divided into strata and a simple random sample is carried out in each group
- Used when sample is large and population is naturally divided into groups
How to carry out a Stratified Sample?
- Find the total number of population
- Obtain the same proportion from each strata by dividing sample size by population size and then multiplying answer by the sample size given in question
- Number the workers in each strata
- Use a random number generator to produce the required quantity of random numbers
Advantages of Stratified Sampling
- Sample accurately reflects population structure
- Proportional representation of groups within population
Disadvantages of Stratified Sampling
- Population must be clearly classified into distinct strata
- Sampling frame needed
What are the two types of non random sampling:
- Quota sampling
- Opportunity sampling
What is Quota sampling?
Where a researcher selects a sample that reflects the characteristics of the whole population
Advantages of Quota Sampling
- Allows a small sample to be representative of the population
- Quick, easy and inexpensive
- Easy comparison between different groups within a population
Disadvantages of Quota Sampling
- Can introduce bias
- Population must be divided into groups which can be costly or inaccurate
- Increasing scope of study increases number of groups and, which adds time and expenses
What is Opportunity sampling?
Where sample is taken from people who are available at the time of study and who fits the criteria they are looking for
Advantages of Opportunity sampling
- Easy and inexpensive
Disadvantages of Opportunity Costs
- Unlikely to provide a representative result
- Highly dependent on individual research
What is a continuous variable?
- A variable that can take any value in a given range
What is a discrete variable?
- A variable that can only take specific values
What is the class width?
The difference between upper and lower class boundaries
