Unit 3: KA2 - Experimentation Flashcards
Define the term ‘reliability’
Refers to whether a procedure yields consistent values each time it is repeated or replicated.
Define the term ‘validity’
variables are controlled, so that any measured effect is likely to be due to the independent variable.
Define the term ‘accuracy’
A measure of how close the data sets are to the true value.
Define the term ‘precision’
Measured values are close to each other.
How are pilot studies used?
to help plan procedures, assess validity and check techniques.
What are the advantages of pilot studies?
- They allow the evaluation and modification of experimental design.
- can ensure an appropriate range of values for the independent variable.
- Establishment of number of repeat measurements required for representative value
Describe the types of variables.
- Dependent: Factor that changes as a result of the independent variable changing
- Independent: Factor being changed in a n investigation
- Confounding: Due to complexities of biological systems, other variables besides the independent variable may affect the dependent variable.
Describe the two categories that dependent and independent variables fall under.
Discrete: Distinct group
Continuous: Can be measured
Describe an experiment in terms of variables.
Experiments involve the manipulation of the independent variable by the investigator.
What is the experimental treatment group compared to?
A control group.
What is the term for an experiment which uses multiple independent variables
Multifactorial
Compare Simple and multifactorial experiments
Simple: - Easier to control confounding variables
- good for lab base studies
- simple protocols
- findings may not be applicable to a wider setting
Multifactorial: - Difficult to control confounding variables
- Can look at how different systems interact
- Complex protocol
- Useful for human/animal studies
Why may investigators use existing groups?
So there is no truly independent variable
Describe an observational study.
Features existing groups, so the independent variable is not directly controlled by the investigator, for ethical or logistical reasons.
Describe the advantage and disadvantage of observational studies
- Good at detecting correlation
- Since no direct hypothesis is tested, less useful at determining causation
What must be done with confounding variables in an investigation?
Must be held constant if possible, or at least monitored, so their effect on the results can be accounted for in the analysis.
What experimental design can be used to counteract confounding variables that cannot be easily controlled, and how does it work?
- Randomised block design
- Groups can be distributed in such a way that any confounding variable is likely to be the same across the treatment and control groups.
Why are controls used?
For comparison with the results of treatment group
Describe the types of controls.
Negative: Provides results in the absence of treatment
Positive: Treatment added to check that the system can detect a positive result when it occurs.
Define the term ‘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.
Define the term ‘placebo’.
Placebos can be included as a treatment without the presence of the independent variable being investigated
Define the term ‘placebo effect’.
Measurable changes in the dependent variable as a result of the patient’s expectations, rather than changes in the independent variable
Define the term ‘in vivo’
Refers to experimentation using a whole, living organism
Define the term ‘in vitro’
Refers to the technique of performing a given procedure in a controlled environment outside of a living organism.
Describe the advantages and disadvantages of in vivo
Advantages:
- Can observe overall effects
- Effects are in real life context
Disadvantages:
- Variables are not easy to control
- Can be dangerous, so models used first
Describe the advantages and disadvantages of in vitro
Advantages:
- Variables are easy to control
- Can determine causation
Disadvantages:
- May not give a clear idea of overall effect
- Findings can be misleading
When is sampling used?
Where it is impractical to measure every individual, a representative sample of the population is selected.
What does a sample size depend on?
The natural variation in a population.
More variable populations require a larger sample size.
How do you determine if a sample is representative?
It should share the same mean, and the same degree of variation around the mean as the population as a whole
Name the three types of sampling.
- Stratified
- Systematic
- Random
Describe stratified sampling.
The population is divided into categories that are then sampled proportionally
Describe Systematic sampling
Members of a population are selected at regular intervals.
Describe Random sampling
Each individual has an equal chance of being selected..
What may cause variation in experimental results?
- reliability of measurement methods
- inherent variation in specimens
How would you test the reliability of measuring instruments?
repeated measurements of a single datum point. This indicates precision, but necessarily accuracy.
How is natural variation in biological material used determined?
By measuring a sample of individuals from the population
How can you determine a reliable mean value of a population?
If you repeat the same measurements on each individual you can calculate a reliable mean value.
The mean of these repeated measurements will give an indication of the true value being measured.
What does the range of values show?
The extent of variation in the results.
Narrow range means low variation
Wide range means high variation
Describe the differences between replicates and repeats.
Replicates:
- Separate and independent to original procedure
- Fresh materials required
Repeats:
- Part of original procedure
- Same materials used
Define the term ‘independent replicate’
When an experiment is repeated as a whole.
How can independent replicates be used?
Independent data sets can be compared to determine reliability.
Name the three types of data.
- Qualitative
- Quantitative
- Ranked
Describe Qualitative data
Qualitative data is subjective and descriptive
Deals with descriptions
Describe Quantitative data
Quantitative can be measured objectively, usually with numerical value.
Describe 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 does the type of data measured impact?
They way the data is presented
What can error bars communicate?
- How spread the data are around the mean
- The reliability of the mean value
- Likelihood of there being a significant difference between data sets
Define the term ‘correlation’
correlation exists where there is a relationship between two variables.
Describe the types of correlation
- Negative: Increase in one variable results in the decrease of the other variable
- Positive: Increase in one variable results in the increase of the other variable
- No correlation: No relationship between variables
Describe the strength of correlation
The strength of correlation is proportional to the spread of values from the line of best fit
