Key Area 2 - Experimentation Flashcards
Experimentation
Define validity
Validity: variables controlled so that any
measured effect is likely to be due to the
independent variable.
Define reliability
Reliability: consistent values in repeats and
independent replicates.
Define accuracy
Accuracy: data, or means of data sets, are
close to the true value.
Define precision
Precision: measured values are close to each other.
Pilot Study
What is a pilot study used for?
Integral to the development of an
investigation, a pilot study is used to help
plan procedures, assess validity and check
techniques.
What does a pilot study allow?
This allows evaluation and modification of
experimental design.
What can a pilot study ensure?
The use of a pilot study can ensure an
appropriate range of values for the
independent variable.
In addition, it allows the investigator to
establish the number of repeat
measurements required to give a
representative value for each independent
datum point.
Experimental design - Independent & Dependent Variables
What is an independent variable?
An independent variable is the variable that is changed in a scientific experiment.
Independent and dependent variables can be continuous or discrete.
What is a dependent variable?
A dependent variable is the variable being
measured in a scientific experiment.
Independent and dependent variables can be continuous or discrete.
What do experiments involve?
Experiments involve the manipulation of the independent variable by the investigator.
What is the experimental treatment group compared to?
The experimental treatment group is
compared to a control group.
Explain the use and limitations of simple (one independent variable) and multifactorial (more than one independent variable) experimental designs
The control of laboratory conditions allows
simple experiments to be conducted more
easily than in the field. However, a drawback of a simple experiment is that its findings may not be applicable to a wider setting.
A multifactorial experiment involves a
combination of more than one independent variable or combination of treatments.
What are observational studies good at detecting?
Observational studies are good at detecting
correlation, but since they do not directly test a hypothesis, they are less useful for
determining causation.
In observational studies the independent
variable is not directly controlled by the
investigator, for ethical or logistical reasons.
Experimental design - Confounding variables
Due to the complexities of biological systems, other variables besides the independent variable may affect the dependent variable.
Why must confounding variables be held constant as much as possible?
These confounding 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.
In cases where confounding variables cannot easily be controlled, a randomised block design could be used.
Explain randomised blocks of treatment and control groups
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.
Experimental design - Controls
What are control results used for?
Control results are used for comparison with the results of treatment groups.
Name the two types of controls used
Negative and positive controls may be used.
Explain a positive and negative control
A positive control is a treatment that is included to check that the system can detect a positive result when it occurs.
The negative control provides results in the
absence of a treatment.
What is the use of a placebo?
Placebos can be included as a treatment
without the presence of the independent
variable being investigated.
Explain the placebo effect
Placebo effect is a measurable change in the dependent variable as a result of a patient’s expectations, rather than changes in the independent variable.
Experimental design - In Vivo & In Vitro Studies
Explain in vitro
In vitro refers to the technique of performing a given procedure in a controlled environment outside of a living organism.
Examples of in vitro experiments: cells
growing in culture medium, proteins in
solution, purified organelles.
Give advantages and disadvantages of in vitro
Advantages: less expensive, less time consuming.
Disadvantages: less precise, incomplete representation of the in vitro system.
Explain in vivo
In vivo refers to experimentation using a
whole, living organism.
Give advantages and disadvantages of in vivo
Advantages: more precise, accurate representation of in vivo.
Disadvantages: expensive, more time consuming.
Sampling
Explain random sampling
In random sampling, members of the
population have an equal chance of being
selected.
Explain systematic sampling
In systematic sampling, members
of a population are selected at regular
intervals.
Explain stratified sampling
In stratified sampling, the
population is divided into categories that are then sampled proportionally.
Reliability
Explain the precision and accuracy of repeated measurements
The reliability of measuring instruments or
procedures can 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.
Explain how the natural variation in the biological material being used can be determined
The natural variation in the biological material being used can be determined by measuring a sample of individuals from the population.
What will the mean give?
The mean of these repeated measurements will give an indication of the true value being measured.
What is the range of values?
The range of values is a measure of the
extent of variation in the results.
If there is a narrow range then the variation is low.
What should be carried out to produce independent data sets.
Independent replication should be carried out to produce independent data sets.
Overall results can only be considered
reliable if they can be achieved consistently.
What should independent data sets be
compared to to determine what?
These independent data sets should be
compared to determine the reliability of the results.
Presentation of Data
What do discrete and continuous variables give rise to?
Discrete and continuous variables give rise to qualitative, quantitative, or ranked data
Explain qualitative data
Qualitative data is subjective and descriptive.
Explain quantitative data
Quantitative data can be measured
objectively, usually with a numerical value.
Explain ranked data
Ranked data refers to the data transformation in which numerical values are replaced by their rank when the data are sorted from lowest to highest.
What exists if there is a relationship
between two variables?
Correlation exists if there is a relationship
between two variables.
What is correlation?
Correlation is an association and does not
imply causation. Causation exists if the
changes in the values of the independent
variable are known to cause changes to the
value of the dependent variable.
What is a positive correlation?
A positive correlation exists when an
increase in one variable is accompanied by
an increase in the other variable.
What is a negative correlation?
A negative correlation exists when an
increase in one variable is accompanied by a decrease in the other variable.
Explain the strength of correlation
Strength of correlation is proportional to
spread of values from line of best fit.
