Required Practical 12 - Sampling Flashcards
Explain why it is important to use a statistical test in analysing the results of an investigation
- results may be due too chance
- confirm difference is significant
- in order to accept or reject null hypothesis
Describe how you would place quadrats at random
- random number generator on calculator
- to determine coordinates to place quadrat in a gridded area
Describe how you would decide the number of quadrats to use in order to collect representative data
- enough to carry out a statistical test
- large enough to be reliable and collect in available time
- calculate running mean
Explain why biologists collect data randomly
- avoid bias
- to collect representative data
- so statistical tests can be calculated
Explain why it is important to check the repeatability of measurements
- increases reliability of measurements
- differences less likely to be due to measurement error / anomalies
Describe how you could use a scatter diagram to check the repeatability of measurements made by two observers
- plot one set of results against the other
- expect to see points lying close to line
OR - plot both sets against variable
- look for overlapping/ corresponding points
Suggest precautions taken when carrying out sampling
- allow sufficient time to elapse before taking further samples so vegetation can recover from trampling
- study organisms in situ or take minimum number and return
Evaluate density in measuring abundance of a species
- most accurate
- time consuming
- not suitable when there are too many individuals / individuals are difficult to identify
Evaluate percentage cover (% area of quadrat) in measuring abundance of a species
- more accurate than frequency but less time consuming compared to density
- subjective so unreliable
- does not consider overlapping individuals
Evaluate frequency (% squares in quadrat) in measuring abundance of a species
- quick, basic overview
- inaccurate
- does not consider overlapping individuals
Draw a conclusion using data provided
Give BALANCED Argument
- correlation data shows
- state if correlation is weak or strong
- give anomalous examples
- sample size small so unreliable
- other factors not considered
- cannot be sure since no statistical analysis
Suggest precautions taken when sampling
- avoid trampling on vegetation
- allow sufficient time to elapse before further studies
- study organisms in situ / remove and return and minimum amount
State when to use quadrats and transects
Quadrats - uniform distribution
Transects - distribution changes over an area
Suggest why a certain number of samples is taken
- too many would be too time-consuming
- too few would be unreliable and insufficient to eliminate anomalies