Sampling Flashcards
Define sampling
Taking data from a small part of a large population and then scale up to fit the total population. Researchers use a sampling method to prevent bias.
What is random sampling?
Locations chosen by chance.
Outline the strengths of random sampling
Removes human bias when selecting of sites/population - where may want to select sites that confirm hypotheses. Everything has an equal chance of being selected.
Outline the weaknesses of random sampling
If sample size is small may it may be unrepresentative result.
No guarantee that the sample will be representative of the population.
What is systematic sampling?
Locations chosen at equal intervals.
Outline the strengths of systematic sampling
Accurately shows continuous changes e.g. velocity across a river/ people along a road.
Can be more accurate than random sampling as avoids the chance that a random sample only selects from one part of a population.
Quick/ convenient because you have a system to follow.
Representative data of what’s happening at the time.
Unlikely to miss variations/anomalies as cover whole area.
Outline the weaknesses of systematic sampling
Can pick bias as sampling every 50 cm or so may be crossing points for pedestrians etc.
Access at regular intervals may be impossible (e.g. due to private land/ unsafe)
What is stratified sampling?
Total population divided into smaller groups (strata) an equal proportion to those in the total population are used.
Outline the strengths of stratified sampling
Ensures all areas/types/categories are represented.
Outline the weaknesses of stratified sampling
Difficult to know which subsets of data to include without a pilot study or prior use of secondary data.
Access to specific sites may be difficult.
What is opportunistic sampling?
Selecting anyone who is available and willing to take part.
Outline the strengths of opportunistic sampling
Less time consuming; easiest method to use. Allows access to sites that are safe/on public land.
Outline the weaknesses of opportunistic sampling
BIASED. Data is unlikely to accurately represent the population.
What is transect sampling?
Data collected along a line.
Outline the strengths of transect sampling
Show continuous change.
