Experimentation 3.2 Flashcards
what does validity relate to?
variables that are controlled so that any measured effect is likely to be due to the independent variable
what can variables be?
continuous os discrete
what does reliability relate to?
the confidence in the data and obtaining consistent values in repeats and independent replicates
what does accuracy relate to?
how close to the true value data, or means of data sets, are
what does precision relate to?
how close measured values are to each other
what is a pilot study used for?
- to help plan procedures
- assess validity
- check techniques
- it is integral to the development of an investigation
what does a pilot study allow?
the evaluation and modification of an experimental design
what can the use of a pilot study ensure?
-an appropriate range of values for the independent variable
- can help establish the number of repeat measurements required to give a representative value for each independent datum point
what is the independent variable?
the variable that is changed in a scientific experiment
what is the dependent variable?
the variable that is being measured as the results of a scientific experiment
what do experiments involve?
the manipulation of an independent variable by the investigator
what is the experimental group compared to?
a control group
what is a simple experimental design?
one in which there is one independent variable
what is a multifactorial design?
has more than one independent variable or a combination of treatments
what happens if investigators use experimental groups that already exist?
there will be no truly independent variable
what does the control of laboratory conditions allow?
simple experiments to be conducted more easily than n the field
what are drawbacks?
findings that ay not be applicable to a wider setting
what are observational studies good at detecting?
correlation
what are observational studies not good at determining and why?
causation as they do not directly test a hypothesis
what is not being directly controlled by the investigator for ethical or logistical reasons in observational studies?
the independent variable
what may affect the dependent variable due to the complexities of biological systems?
confounding variables
why must confounding variables be held constant if possible or at least monitored?
so that their effect on the result can be accounted for in the analysis
what could be used where confounding variables cannot be controlled easily?
a randomised block design
how can randomised blocks of treatments and control groups be distributed?
in such a way that the influence of any confounding variable is likely to be the same across treatment and control groups
what are control results used for and what types of controls may be used?
the comparison with the results of treatment groups
- negative and positive controls may be used
what does a negative control provide?
results in the absence of a treatment
what is a positive control?
a treatment that is included to check that the system can detect a positive result when it occurs
placebos lacking the independent variable being investigated can be included as a treatment in what?
human trials
what is the placebo effect?
a measurable change in the dependent variable as a result of a human patient’s expectations, rather than changes in the independent variable
what does in vitro refer to?
the technique of performing a given procedure in a controlled environment outside of a living organism
what are examples of in vitro experiments?
- cells growing in a culture medium
- proteins in solution
- purified organelles
what are the advantages of in vitro studies?
- controllable
- repeatable
- rapid
- cheap
- may avoid ethical and regulatory issues
what are the disadvantages of in vitro studies
- extrapolation is difficult
- chronic effects are not tested
what does in vivo refer to?
experimentation using a whole living organism
what are the advantages of in vivo studies?
- simulate real life
- chronic effects can be tested
what are the disadvantages of in vivo studies?
- difficult to control
- slow
- expensive
- may have ethical and regulatory issues
when may a representative sample of a population be selected?
where it is impractical to measure every individual in a population
what determines the appropriate sample size?
he extent of the natural variation within a population
more variable populations require what?
larger sample sizes
what should a representative sample share with the population as a whole?
the same mean and the same degree of variation about the mean
what happens in random sampling?
members of the population have an equal chance of being selected
what happens in systematic sampling?
members of a population are selected at regular intervals because of an environmental gradient
what happens in stratified sampling?
a non-homogenous population is divided into categories called strata that are then sampled proportionally
what may variation in experimental results be due to?
the reliability of measurement methods and/or inherent variation in the specimens
how can the reliability of measuring instruments or procedures be determined?
- by repeated measurements or readings of an individual datum point
- the variation observed indicates the precision of the measurement instrument or procedure, but not necessarily its accuracy
how can the natural variation in the biological material being used be determined?
by measuring a sample of individuals from the population
what does the mean of repeated measurements indicate?
the true value being measured
what us the rage if values measure of?
the extent of variation in the results
what does it mean for the variation if there is a narrow range?
the variation is low
what does the independent replication involve and why is it carried out?
- repeating experimental procedures with a different investigator, or in a different laboratory, or at a different time
- it is carried out to produce independent data sets
how can overall results be considered reliable?
only if they can be achieved consistently
why should independent data sets be compared?
to determine the reliability of the results
