Topic 1: Data Collection Flashcards
(27 cards)
Define the word CENSUS
When every member of a population is included
Give THREE disadvantages of using a census
- Time consuming and expensive
- Can not be used when testing involves destruction
- Large volume of data to process
Define the word POPULATION
The whole set of items that are of interest
Define the word SAMPLE
Small subset of the population intended to represent a population
Give TWO disadvantages of using a sample
- Data may not be accurate
- Data may not be large enough to represent small sub-groups
Give ONE advantage of using a census
- It should give completely accurate results
Give THREE advantages of using a census
- Cheap
- Quick
- Less data to process compared to using a census
Define the term SAMPLING FRAME
A list of sampling inits which may be the whole population or may represent a population as accurately as possible.
Define the term SAMPLING UNIT
Individual member of a population
State TWO reason why someone would use a RANDOM SAMPLING METHOD
- Efforts to avoid bias (prevents sample from being representative of the population)
- Equal chance of being choses
Define the term RANDOM SAMPLING
Simple random sample of size n is one where every sample size n has an equal chance of being selected
Give THREE advantages of using 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
Give TWO disadvantages of using a random sample
- Sampling frame is needed
- Expensive, disruptive and time consuming if sample size is too large
How would LOTTERY sampling be conducted?
Members of simplify frame would be written out on tickets and placed into a ‘hat’. The required number of tickets would then be drawn out.
Define SYSTEMATIC SAMPLING
The required elements are chosen at regular intervals from an ordered list.
How would you carry out systematic sampling on a sample size of 20 being required form a population of 100.
- You would take every FIFTH person (100/20=5).
- The first person will be chosen at random e.g from a random number generator.
- If the first person in number 2 in the list, the remaining sample would be persons, 7 , 12 , 17 , etc…
Give TWO advantages of systematic sampling
- Simple and quick to use
- Suitable for large samples and populations
Define STRATIFIED SAMPLING
The population is divided into mutually exclusive strata (male and females for example) and a random sample is taken from each.
Give the formula associated to stratified sampling
The number sampled in a stratum=( no. of stratum/no. of population ) x Overall sample size
Give TWO advantages of stratified sampling
- Sample accurately relates the population structure
- Guarantees proportional representation of groups within a population.
Give TWO disadvantages of stratified sampling
- Population must be clearly classified into distinct strata.
- Selection within each stratum suffers from the same disadvantages as simple random sampling.
Define the term OPPORTUNITY SAMPLING
It consists of taking the sample from people who are available at the time the study is carried out and two fits the criteria that you are looking for.
Give TWO advantaged of opportunity sampling
- Inexpensive
- Easy and quick to carry out
Give Two disadvantages of opportunity sampling
- Unlikely to give a representative sample
- Highly dependant on individual researcher
