Sampling Flashcards
point sampling
e.g. names on a list or coordinates on a map
linear sampling
e.g. sampling along a line such as transect along dunes or a road
areal sampling
e.g. usually in investigation surveys where a quadrat is used to measure the contents of a 1 metre square area or it could be a grid square on a map
random sampling description
random number tables to select points e.g. sampling stone size in a river
advantages of random sampling
- more statistically useful for subsequent tests, so allows follow up analysis
- no bias
disadvantages of random sampling
- items can be duplicated
- easy to miss important subdivisions
- hard to ensure its truly random
stratified sampling description
-when the parent population or sampling frame is made up of sub sets known as strata of known size. these sub sets make up different proportions of the total , and therefore sampling should be stratified to ensure that results are proportional and representative of the whole
advantages of stratified sampling
- ensures no significant aspect of the sub sets is missed
- very flexible and applicable to most investigations
disadvantages of stratified sampling
- biased
- proportions of sub sets must be known
- can’t make valid statistical inferences
sampling definition
the strategy of collecting data that is representative of the whole population
problems if the sample size is too small
- less reliable averages can be taken
- more affected by anomalies
- biased
- anything less than 30 doesn’t provide valid conclusions
- statistical tests can’t be done
- might miss something
- patterns/trends are disorted