4.2.1 b types of sampling Flashcards
What is sampling?
Taking measurements of a limited number of individual organisms present in a particular area
What can sampling be used for?
To estimate the number of organisms in an area without having to count them all
What is the abundance of the organism?
Number of individuals present in an area
Another use of sampling is?
To measure a particular characteristic of an organism
What is random sampling?
Selecting individuals by chance so each individual in the population has an equal likelihood of selection
How do you decide which organism to study in random sampling?
Random number tables or computers can be used
What is non- random sampling?
Where the sample is not chosen at random
Three main non-random sampling techniques
Opportunistic
Stratified
Systematic
What is opportunistic non-random sampling?
Using organisms that are conveniently available
What is stratified non-random sampling?
Where some populations are divided into a number of strata based on a parti characteristic. A random sample is taken from each of these strata proportional to it’s size.
What is a strata?
Sub-group
What is systematic non-random sampling?
Different areas within an overall habitat are identified which are then sampled separately
Often carried out using a line or a belt transect
what is a line transect?
marking a line along the ground between two poles and taking samples at specified points
what is a belt transect?
two parallel lines are marked and samples are taken of the area between the two lines
why is a sample never entirely representative of the organisms present?
sampling bias- selection process may be biased by accident or deliberately
chance- the organisms selected may not be representative of the whole population- the greater the number of individuals studied, the lower the probability that chance will influence the result so the larger the sample size, the more reliable the result
