Sampling terminology Flashcards
Sampling frame
The study area or group from which the sample is selected: e.g. area on an OS map, electrical register, telephone directory, every person entering a shopping centre.
Target population
Total set of measurements relevant to a study e.g. all possible measurements of pebble size from a beach which are useful for the investigation
Sampled population
Measurements for the area which is accessible to the investigation e.g. pebbles which are exposed on the surface of a beach
Sample size
The number of measurements in the sample. For further statistical analysis, this is usually taken to be a minimum of 30.
Population parameter
A true summary measurement of the characteristics of the target population e.g. mean size of all the pebbles on the beach. If the parameter is based on a sample, it is only an estimate.
Bias
This occurs when the sample measurement over- or under - estimates the population parameter.
It may be introduced unconsiously
Sampling error
The difference between a sample estimate and the population parameter
Representative sample
A sample that minimises bias
Examples of spatial sampling:
- Point sampling
- Line sampling
- Area sampling
Point sampling
Selection of a series of specific points within an area
Line sampling
Sampling along a line
Area sampling
A selection of sampling squares
What types of sampling are there?
- Random
- Systematic
- Stratified
- Pragmatic
