Unit 3 - section 2 Flashcards
What is a pilot study?
Study carried out to test the experimental procedures before commencing the study
What is usually done as a result of carrying out a pilot study?
Evaluation and modification of experimental procedures
What are the 5 aspects of experimental design that can be assessed/developed during a pilot study?
Effectiveness of technique and gives experimenter experience with procedures
Range of values of independent variable
Identification and control if confounding variables
Number of repeats and replications required
Suitable timescale for procedures
What is a confounding variable?
Any variables that may affect the dependent variable other than the independent variable
Why is it important to monitor a confounding variable if it cannot be kept constant?
So it’s affect can be considered during results
How can the effects of a confounding variable that is difficult to keep constant be minimised?
By blocking experimental and control groups so that an even distribution from each block are exposed to each independent variable
What are discrete and continuous variables?
Discrete variables - data that can only take on certain individual values eg cell number in Petri dish
Continuous variables - data that can take on any value in a certain range eg temperature
What are the 3 types of data that can be gathered?
Quantitative - information that can be measured in numbers
Qualitative - information that involves descriptions. It can be observed but cannot actually be measured
Ranked - data is revalued and given a rank instead of the actual measurement/observation
What can the type of variable and data gathered affect when presenting or analysing findings?
The way the data is presented
Discrete - in bar graph
Continuous - in line graph
What is an independent variable?
Factor being changed in an investigation
What is an experimental treatment group compared with?
A control group
What is a dependent variable?
Factor that changes as a result of the independent variable changing
How many variables are altered in simple experimental design?
I variable
How many variables are altered in multifactorial experimental design?
More than 1 variable
What is an advantage and a disadvantage of simple and multifactorial experimental designs?
Advantage simple - usually in vitro so easier to control variables than in the field
Disadvantage simple - findings may not be accepted in the wider scientific community
Advantage multifactorial - lots of data can be obtained which can show complex interactions
Disadvantage multifactorial - usually in vivo so difficult to control
What do vivo and vitro mean?
Vivo - natural habitat
Vitro - in a lab
Are vivo or vitro experiments more complex?
Vivo are more complex
What is an observational study?
Uses groups that already exist so there is not a true independent variable as the observer is not causing the change
What are the limitations of observational study?
It can determine correlation but not causation
What is a control and what is its purpose in an experiment?
Controls are not exposed to the experimental conditions and are hard to compare to the treatment groups to identify false positives
What is a positive control?
Group that is not exposed to the experimental treatment but to another treatment that is known to produce the expected effect
What is a negative control?
Group that is not exposed to the experimental treatment or any other treatment that is expected to have an effect
What is a representative sample and when would it be used?
Small sample of the whole population that is used when it is not practical to sample every single individual in a population
What determines an appropriate sample size?
Natural variation in a population
Larger population requires a larger sample size
Compare a representative sample to the population as a whole?
Should have the same mean value and the same variation about the mean
What is random sampling?
Each individual has an equal chance of being selected
What is systematic sampling?
Population is sampled at set intervals
What is stratified sampling?
Sample is split and then divided proportionally
What are 2 possible reasons for variation in experimental results?
Reliability of measurement
Natural variation of specimen
How can the reliability of measuring instruments or procedures be determined?
By how consistent the results are
Reliability is increased by repeating measurements or readings
What does the variation observed in an experiment indicate?
The precision of the measurement instrument or procedure.
It does not necessarily indicate accuracy
What does accuracy mean when describing experimental measurements?
How close the data is to the true value
What does the term precision mean when describing experimental measurements?
How close the data values collected are to the other data values collected
How can the natural variation in living material be determined?
By taking a representative sample and calculating the mean
What does the mean of a set of data give an indication of?
The true value of the total population
What is an independent replicate?
When an experiment is repeated as a whole completely separate from the other experiment
Why is an independent replicate required?
Results are only seen as being reliable if they can be achieved consistently in independent replicates
