Y1, C1 - Data Collection Flashcards
What is a population
The whole set of items that are of interest
What is a sample
Some subset of the population intended to represent the population
What is a sampling unit
Each individual thing in the population can be sampled as a sampling unit
What is a sampling frame
Sampling units of a population are individually named to form a list called the sampling frame
What is a census
Data collected from the entire population
Census advantages and disadvantages (compared to a sample)
+ Completely accurate results
- Time consuming and expensive
- Cannot be used when it involves destruction
- Large volume of data to process
Sample advantages and disadvantages (compared to a cenus)
+ Cheaper
+ Quicker
+ Less data to process
- Data may not be accurate
- Data may not be large enough to represent small sub-groups
What are the 3 types of random sampling
Simple Random Sampling
Systematic Sampling
Stratified Sampling
What is random sampling
Each sampling unit in a sampling frame has an equal chance of being chosen to avoid bias
Pros and cons and how to carry out Simple Random Sampling
+ Bias free
+ Easy and cheap
+ Each number has a known chance of being selected
- Not suitable for large population size
- Sampling frame needed
Assign each item an identifying number. Random generator the numbers
Pros and cons and how to carry out Systematic Sampling
+ Simple and quick
+ Suitable for large samples
- Sampling frame needed
- Can introduce bias if sampling frame isn’t random
Take every kth elements where k = population size (N) / sample size (n) starting at random item between 1 and k
Pros and cons and how to carry out Stratified Sampling
+ Reflects population structure
+ Guarantees proportional representation of groups
- Population must be clearly classified into distinct strata
- Selection within each stratum suffers from same disadvantages as simple random sampling
Same proportion (sample size (n) / population size (N)) from each strata
What is a strata
A distinct group
What are the 2 types of non-random sampling
Quota sampling
Opportunity / Convenience Sampling
What is a quota
A fixed share / number of something
When can’t we do a random sample
When we don’t have a sampling frame
Pros and cons and how to carry out quota sampling
+ Allows small groups to still be representative of population
+ No sampling frame required
+ Quick, easy, inexpensive
+ Allows for an easy comparison between different groups in population
- Bias
- Population must be divided into groups which can be costly or inaccurate
- Non-responses are not recorded
- Increasing scope of the study increases number of groups therefore time / expense
Stratified sampling but then the interviewer selects the actual sampling units
Pros and cons and how to carry out opportunity / convenience sampling
+ Easy to carry out
+ Inexpensive
- Unlikely to provide a representative sample
- Highly dependent on individual researcher
Interviewer selects the actual sampling units according to the set criteria
What are the two types of data
Qualitative
Quantitative
What is quantitative data
Numerical values
What is qualitative / categorical data
Non-numerical values
What are the two types of quantitative data
Discrete
Continous
What is discrete data
Can only take specific values
What is continuous data
Can take any decimal value
What is a trace value (tr)
When the value is too low to be measured (under the minimum measuring unit, e.g. under 1cm on a metre ruler)
