3e- Experimental design Flashcards
What is the difference between the independent and dependent variable?
Independent variable= the variable that is changed in an experiment
Dependent variable= the variable being measured in an experiment
What can independent and dependent variables be?
Discrete or continuous
What do experiments involve?
The manipulation of the independent variable by the investigator
What is the experimental group in a experiment compared to?
A control group
What is a simple experiement?
One where only one independent variable is investigated (e.g. measuring the effect of temperature on enzyme activity)
What is an advantage and a drawback of a simple experiment?
Advantage= easy to control conditions of the lab and so allows the experiment to be conducted more easily in the field
Drawback= its findings may not be applicable to a wider setting
What is a multifactorial experiment and what may investigators use in them?
Involves a combination of more than one independent variable or combinations of treatments. Investigators may use groups that already exist, so there is truly no one independent variable
What happens in observational studies?
The independent variable is not directly controlled by the investigator, for ethical or logistical reasons. Instead they use pre-existing groups to investigate correlation between variables
What are observational studies good for?
Detecting correlation but since theydo not directly test a hypothesis, they are less useful for detecting causation
What are confounding variables?
Due to the complexities of biological systems, other variables besides the independent variable may affect the dependent variable, these other variables are confounding variables
What must happen to any confounding variables?
They must be held constant if possible, or at least monitored so that their effect can be accounted for in analysis
What could be used in experiments where confounding variables cannot be easily controlled?
A randomised block design
What is a randomised block design?
Blocks of treatments and controls are distributed in such a way that the influence of any confounding variable is likely to be the same across the treatment and control groups
What are control groups used for?
Comparison with the results of treatment groups, it is used to prove that it is the independent variable which is the cause of any effect seen in results
What does a negative control do?
Provides results in the absence of treatment (e.g. adding a denatured enzyme to substrate when studying the effect of that enzyme on that substrate)
