3.2c - Experimental Design Flashcards
The independent variable is…
the one you change
The dependent variable is…
the one you measure
Independent and dependent variables can be…
continuous or discrete
Experiments involve the manipulation of the…
independent variable by the investigator
The experimental treatment group is compared to…
a control group
Simple experimental designs have…
one independent variable
Multifactoral experimental designs have…
more than one independent variable
A benefit of simple experiments is that…
the control of laboratory conditions allows simple experiments to be conducted more easily than in the field
A limit of simple experiments is that…
their findings may not be applicable to a wider setting
A benefit of multifactoral experiments is that…
they are more relevant to complex biological systems
A limit of multifactoral experiments is that…
they are more complex to analyse and require careful experimental design and complex statistics for valid conclusions to be drawn
In an experiment, investigators may use groups that already exist so that…
there is no truly independent variable
In observational studies the independent variable is…
not directly controlled by the investigator, for ethical or logistical reasons
Observational studies are good for…
detecting correlation
Observational studies are less good for…
determining causation because they do not directly test for a hypothesis
Causation exists if…
changes in the values
of the independent variable are known to cause changes to the value of the dependent variable
Other variables (confounding variables) besides the independent variable may affect the dependent variable due to…
the complexities of biological systems
Confounding variables must be held constant if possible, or monitored so…
that their effect can be accounted for in the analysis
Any change in confounding variables any affect…
in the validity of any observed change in the dependent variable
What can be used in cases where confounding variables cannot be easily controlled?
a randomised block design
Randomised blocks of treatment and control groups can be distributed in such a way that…
the influence of any confounding variable is likely to be the same across the treatment and control groups
Control results are used for…
the comparison with the results of treatment groups
Controls the determine the…
validity of any change in the dependent variable
What 2 controls can be used in experiments?
positive and negative
Negative controls…
provide results in the absence of a treatment eg placebo
Positive controls…
check that the system can detect a positive result when it occurs
Placebos can be included as a treatment without…
the presence of the independent variable being investigated
Placebo effect is…
measurable change in the dependent variable as a result of a patient’s expectations, rather than changes in the independent variable
In vitro refers to…
the technique of performing a given procedure in a controlled environment outside of a living organism
3 examples of in vitro experiments
- cells growing in culture medium
- proteins in solution
- purified organelles
In vivo refers to…
experimentation using a whole, living organism
An advantage of an in vitro study is…
that it is easily controlled
A disadvantage of an in vitro study is…
that its relevance may be limited in vivo
An advantage of an in vivo study is…
that it allows possible side effects to be seen
A disadvantage of an in vivo study is…
that it can be unethical
