Experimentation- Experimental Design Flashcards
What is a variable?
Any factor that can be controlled, changed or measured in an experiment. Variables can be discrete or continuous, independent or dependent
What is a continuous variable?
It can take on infinitely many uncomfortable values. For example length, concentration, wavelength
What is a discrete variable?
It can have a finite range of values. For example colour, presence/absence
During an experiment what variable is manipulated by the investigator?
The independent variable
What is an independent variable?
The variable that is changed in a scientific experiment
What is a dependent variable?
The variable that is measured in a scientific experiment
In an experiment what will an experimental treatment group be compared to?
A control group
What are the two ways that experiments be designed?
Either simple or multifactorial
What is a simple experiment?
An experiment with one independent variable
What is a multifactorial experiment?
An experiment with more than one independent variable or treatment
What conditions are better for simple experiments?
The control of laboratory conditions allows simple experiments to be conducted more easily than in the field.
What is a drawback of a simple experiment?
Its findings may not be applicable to a wider setting
What is an observational study?
Sometimes investigators may use groups that already exist so there is no truly independent variable. In observational studies the independent variable is not directly controlled by the investigator for ethical or logistical reasons
What is an example of an observational study?
An observational study is one investigating the relationship between smoking and lung cancer. An experimental group of people who had been smoking for 20 years would be compared with a control group of people who had never smoked. This is the only viable way of recruiting participants as it would be unethical to ask a group of individuals to smoke for 20 years to allow comparison with a control group. Recruiting experimental groups in this way allows researchers to study long term effects of certain variables (e.g. effects lasting decades) which may not otherwise be possible
What are observational studies are good at detecting?
Correlation
What are observational less useful for determining and why?
They don’t directly test a hypothesis so they are less useful for determining causation
What is a confounding variable?
Variables other than the independent and dependent variables that may affect the results of an investigation and therefore need to be considered during the investigation
What must be considered about confounding variables?
Due to the complexities of biological systems other variables besides the independent variable may affect the dependent variable. These cofounding variables must be held constant if possible or at least monitored so that their effect on the results can be accounted for in the analysis
When would a random block design be used?
In cases where confounding variables cannot be easily controlled. It is a form of stratified sampling
How are randomised blocks of treatment and control groups 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 is a control?
Experimental treatment groups are often compared with a control group. Control is an experimental group where no treatment is given
What are control results used for?
Comparison with the results of treatment groups.
What are the two categories of control that can be used?
Negative controls and positive controls
What is a negative control?
Provides the results in the absence of treatment
What is a positive control?
A treatment that is included to check that the system can detect a positive result when it occurs e.g. ELISA
What is a placebo?
A placebo can be included as a treatment without the presence of the independent variable being investigated
What is the placebo effect?
It is a measurable change in the dependant variable as a result of a patient’s expectations rather that changes in the independent variable
What is in vivo?
Experimentation using a whole living organism. Translating from Latin to ‘in the living’
What is in vitro?
Preforming a given procedure in a controlled environment outside of a living organism. Translates from Latin to ‘in the glass’
What is an example of in vitro?
Cells growing in culture medium proteins in solution purified organelles
What is a advantage of in vitro?
Better control of your experiment and any confounding variables
What is a disadvantage of in vitro?
Not possible for many biological studies
What is a advantage of in vivo?
You get a better idea of what is going on inside the cell or organism
What is a disadvantage of in vivo?
Living organisms show great variability which can’t really be controlled
What are clinical trials?
Studies that investigate the effectiveness of new medicines or treatments for humans
Why must trials be care fully controlled?
In order to be sure that the observed improvements (for example a medical condition) are due to the test medication and not another factor
What is a placebo?
A type of negative control which can be given to human control group on a clinical trial. Typically groups of trial participants will be randomly assigned to either the test or placebo group
What is a double blind study design?
When neither the researcher nor the trial participant will know which group they are in until the end of the study. It eliminate bias
What is the placebo effect?
It is a measurable change in the dependent variable as a result of a patient’s expectations rather that changes in the independent variable. Which accounts for psychological effects that trial participants may experience purely through the process of being treated
