11.2 Types of sampling Flashcards
what is sampling?
taking measurements of individual organisms in an area
why is sampling done?
it is too time consuming to analyse every organism in an area
instead a sample is taken to allow you to make an estimate
what are the two types of sampling?
random
non-random
what is random sampling?
collecting individuals by chance
eliminates bias
main method of random sampling
using a computer to give random number for a specific section in an area
you would sample that section
what is non-random sampling?
sample is not taken at random to ensure all areas are sampled
types of non-random sampling?
systematic
opportunistic
stratified
oppurtunistic
samples are simply chosen by an investigator based off of convinence
cons of opportunistic
does not represent the entire population, only the chosen sample
systematic
samples are taken at fixed intervals to cover an entire area
makes the sample more representative of the entire area
how is systematic sampling often carried out?
using a line and belt transect
stratified
population is divided into sub-groups
these sub-groups are then proportionally sampled based on their size compared to the entire population
why is a sample never fully representative of a population?
sampling bias
chance
sampling bias
selection process will always be biased either accidentally or on purpose
human involvement = more bias
how is the reliability of a sample increased?
increasing the sample size reduces the possibility of chance
therefore results are more reliable
