UNIT 3 - KA2 Flashcards
Validity
variables controlled so that any measured effect is likely to be due to the independent variable.
Reliability
consistent values in repeats and independent replicates.
Accuracy
data, or means of data sets, are close to the true value.
Precision
measured values are close to each other.
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 are the benefits of a pilot study
This allows evaluation and modification of experimental design
What does the use of a pilot study ensure
The use of a pilot study can ensure an appropriate range of values for the independent variable
What do pilot study allow the investigator to establish
In addition, it allows the investigator to establish the number of repeat measurements required to give a representative value for each independent datum point
What is an independent variable
An independent variable is the variable that is changed in a scientific experiment.
What is a dependant variable
A dependent variable is the variable being measured in a scientific experiment.
What can independent and dependant variables be
Independent and dependent variables can be continuous or discrete
What should be manipulated in experiments
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
Negative control
Provides results in the absence of a treatment
Positive control
A treatment that is included to check that the system can detect a positive result when it occurs
What does the control of laboratory conditions allow
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
However, a drawback of a simple experiment is that its findings may not be applicable to a wider setting.
What is a simple experimental design
One independent variable
What is a multifactorial experiment
More than one independent variable
What does a multifactorial experiment involve
A multifactorial experiment involves a combination of more than one independent variable or combination of treatments.
What is 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.
What is in vitro technique
In vitro refers to the technique of performing a given procedure in a controlled environment outside of a living organism
What are examples of in vitro experiments
Examples of in vitro experiments: cells growing in culture medium, proteins in solution, purified organelles.
What is in Vivo
In vivo refers to experimentation using a whole living organism
What are advantages of in vitro
- provide data for effects in whole organisms
- allows study of complex interactions
What are disadvantages of in vitro
- expensive and time consuming
- ethical and legislative concerns
- difficult to control confounding variables
- results difficult to interpret
- difficult to prove causation
What are advantages of in vivo
- simpler and less expensive
- easier to control confounding variables
- interpretation of results is simpler
- can demonstrate correlation and causation
What are disadvantages of in vivo
- difficult to extend
- result to whole organisms or different species
- difficult to model complex interactions
What happens when it is impractical to measure every individual
Where it is impractical to measure every individual, a representative sample of the population is selected
What does the extent of natural variation within a population determine
The extent of the natural variation within a population determines the appropriate sample size
What do more variable populations require
More variable populations require a larger sample size
What should a representative sample share the same of
A representative sample should share the same mean and the same degree of variation about the mean as the population as a whole
Why is sample size an important decision
- Sample size is an important decision because it affects your reliability of your results.
What are the three different sampling strategies
- random sampling
- systematic sampling
- stratified sampling
Random sampling
In random sampling, members of the population have an equal chance of being selected.
Systematic sampling
In systematic sampling, members of a population are selected at regular intervals.
What is an example of systematic sampling
Quadrats used every 1M along a transect or every 5th person samples in a population
Stratified sampling
In stratified sampling, the population is divided into categories that are then sampled proportionally.
When is stratified sampling used
Used when sampling habitats that are not uniform eg within a sample area there may be areas of non uniform areas of grass, bushes small trees etc
What is variation in experimental results due to
Variation in experimental results may be due to the reliability of measurement methods and/or inherent variation in the specimens
What is the reliability of measuring instruments or procedures determined by
The reliability of measuring instruments or procedures can be determined by repeated measurements or readings of an individual datum point.
What does the variation observed in repeated measurements indicate
The variation observed indicates the precision of the measurement instrument or procedure but not necessarily its accuracy.
How can the natural variation in biological material being used be determined
The natural variation in the biological material being used can be determined by measuring a sample of individuals from the population
What does the mean of the repeated measurements give an indication of
The mean of these repeated measurements will give an indication of the true value being measured
What is the range of values a measure of
The range of values is a measure of the extent of variation in the results
What happens if there is a narrow range
If there is a narrow range then the variation is low
Why should Independent replication be carried out
Independent replication should be carried out to produce independent data sets
When only can results be considered reliable
Overall results can only be considered reliable if they can be achieved consistently. The independent data sets should be compared to determine the reliability of the results
What do discrete and continuous variables give rise to
Discrete and continuous variables give rise to qualitative, quantitative, or ranked data
What is qualitative data
Qualitative data is subjective and descriptive.
How can quantitative data be measured
Quantitative data can be measured objectively, usually with a numerical value.
What is 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 happens to the independent variable in observational studies
In observational studies the independent variable is not directly controlled by the
investigator, for ethical or logistical reasons
What are observational studies good and less useful for
Observational studies are good at detecting correlation, but since they do not directly test a hypothesis, they are less useful for determining causation
Can other variables besides the independent variable affect the dependant variable?
Due to the complexities of biological systems, other variables besides the independent
variable may affect the dependent variable
Why should confounding variables be controlled
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
What can be used in cases where confounding variables cannot be easily controlled
In cases where confounding variables cannot easily be controlled, a randomised block
design could be used
How can randomised blocks of treatment and control groups be distributed
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.
What does the type of variable being investigate have consequences for
The type of variable being investigated has consequences for any graphical display or
statistical tests that may be used
What is correlation
Correlation is an association and does not imply causation.
When does correlation exist
Correlation exists if there is a relationship between two variables
When does causation exist
Causation exists if the changes in the values of the independent variable are known to cause changes to the value in the dependant variable
When does a positive correlation exist
A positive correlation exists when an increase in one variable is accompanied by
an increase in the other variable.
When does a negative correlation exist
A negative correlation exists when an increase in one variable is accompanied by a
decrease in the other variable.
What is strength of correlation proportional to
Strength of correlation is proportional to spread of values from line of best fit.
