Sampling Flashcards
Population definition
The whole set of items that are of interest
What is a census?
(A&D)
Measures every member of the population
Advantage:
-Accurate result
Disadvantage:
-Expensive, time consuming
-Cannot be used when testing involves destroying items
-Hard to process large quantity of data
What is a sample?
(A&D)
A selection of observations taken from a subset of population
used to find out more info about the population as a whole
Advantage:
-Less time consuming and cheaper
-Fewer people have to respond
-Less data needs to be processed
Disadvantage:
-Data may not be as accurate
-Sample may not be large enough to represent smaller subgroups of population
Sampling units
Individuals of a population
Sampling frame
List of sampling units
Simple random sampling
Random sampling
What it is, advantages and disadvantages
-Each unit has an equal chance of being selected
-Using a random number generator/lottery sampling to generate sample and select items corresponding to the number produced
Advantage:
-Bias free
-Easy and cheap for small samples and populations
-Each sample unit has a known and equal chance of selection
Disadvantage:
-Needs a sampling frame
-Not suitable for large samples and populations
Systematic sampling
Random sampling
What it is, advantages and disadvantages
-Take every kth unit, k= size of population/sample size
-Generate a random number between 1 and k for starting point
Advantage:
-Quick to use
-Can be used for large samples and populations
Disadvantage:
-Needs a sampling frame
-Bias introduced if sampling frame is not random
Stratified sampling
Random sampling
What it is, advantages and disadvantages
-Sample represents the groups (strata) of the population
-(Sample size/ population size)*strata size for each strata
-Pick randomly
number sampled in a stratum= no. in strata/ no. in population * overall sample size
Advantage:
-Reflects population more accurately
-Proportional representation of group within population
Disadvantage:
-Population must be classified in strata
Quota sampling
Non random sampling
What it is, advantages and disadvantages
Interviewer/researcher selects a sample that reflects the characteristics of the whole population
Advantage:
-No sampling frame
-Easy and inexpensive
Disadvantage:
-Not random, potential bias
-Non-responses not recorded
Opportunity sampling
Non random sampling
What it is, advantages and disadvantages
-Quota is filled by those available at the time
Advantage:
-Easy and cheap
Disadvantage:
-Unlikely to be representative
Qualitative data definition
Non numerical
e.g colour, type, shape
Quantitative data definition
Discrete & continuous
Numerical
- Discrete - can only take specific values, e.g. shoe size
- Continuous - can take any decimal value
