Experimentation Flashcards
What is validity?
Variables controlled so that any measured effect is likely to be due to the independent variable.
What is reliability?
Consistent values in repeats and independent replicates.
What is accuracy?
Data, or means of data sets, are close to the true value.
What is precision?
Measured values are close to eachother.
What is a pilot study used to do?
• Help plan procedures, assess validity and check techniques.
• Allows evaluation and modification of
experimental design.
• Ensure an appropriate range of values for the independent variable.
• 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?
The variable that is changed in a scientific experiment.
What is the dependent variable?
The variable being measured in a scientific experiment.
Independent and dependent variables can be one of 2 things, what are they?
Continuous or discrete.
What do experiments involve?
The manipulation of the independent variable by the investigator.
What is the experimental treatment group compared to?
A control group.
Simple experiments:
- changing 1 independent variable
- commonly lab based studies
- simple, variables can be controlled, easy analysis of results.
- findings may not be applicable to a wider setting.
Multifactorial experiments:
- changing more than 1 independent variable
- investigators may use groups that already exist, so there is no truly independent variable.
- examines complex interactions
- time consuming, difficult to control all variables
What are observational studies good at?
Detecting correlation.
What are observational studies bad at?
They are less useful for determining causation. As they don’t directly test a hypothesis.
In observational studies why is the independent variable not directly controlled by the investigator?
For ethical or logistical reasons
Why do confounding variables occur?
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 if possible or atleast monitored?
So that their effect in the results can be accounted for in the analysis.
When is randomised block design used?
In cases where confounding variable cannot be easily controlled.
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 are control results used for?
Comparison with the results of treatment groups.
What is a negative control?
Provides the 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
What are placebos?
They can be included as a treatment without the presence of the independent variable being investigated.
What is the placebo affect?
A measurable change in the dependent variable as a result of a patient’s expectations, rather than changes in the independent variable.
Where is impractical to measure every individual, a. ——— ——— of a population is selected.
Representative sample.
What is in vitro?
Technique of performing a given procedure in a controlled environment outside of a living organism
What is in vivo?
Refers to experimentation using a whole living organism
Advantages of in vitro
- Controlled Environment
- Reproducibility
- Cost effective
- Ethical considerations
- Faster results
- Isolation of variables
- Easier Sample Analysis
Disadvantages of in vitro
- Lack of Biological Complexity
- Limited Predictive Power
- Absence of Metabolism
- External Influences
- Extrapolation Issues,
- Potential for Contamination
- Time-Consuming Setup
Advantages of in vivo
- Biological Relevance
- Metabolic and Enzymatic Effects
- Interaction with Complex Systems
- More Reliable for Drug Testing
- Long-Term Effects Can Be Studied
- More Accurate Dosage Information
- Realistic Response to Environmental Factors
Disadvantages of in vivo
- Ethical Concerns
- Expensive and Time-Consuming
- Complex and Difficult to Control
- Variability Between Organisms
- Regulatory and Legal Restrictions
- Difficult Data Interpretation
- Risk of Adverse Effects
Examples of in vitro experiments:
Cells growing in culture medium, proteins in solution, purified organelles.
When is representative sample of the population selected?
When it is impractical to measure every individual.
What determines the appropriate sample size?
The extent of the natural variation within a population.
More variable populations require —— sample size
Larger
A representative sample should share the same … as the population as a whole
The same mean and the same degree of variation about the mean.
What is random sampling?
Members of the population have an equal chance of being selected.
What is systematic sampling?
Members of a population are selected at regular intervals.
What is stratified sampling?
The population is divided into categories 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.
What indicates the precision of the measurement instrument or procedure but not its accuracy?
The variation in measurements.
How can the natural variation in the biological material being used be determined?
By measuring a sample of individuals from the population.
What will a mean of repeated measurements give you?
An indication of the true value being measured.
What is the range of values a measure of?
The extent of variation in the results.
If there is a narrow range of values then the variation is ——
Low
Independent replication should be carried out to produce…
Independent data sets.
Overall results can only be considered reliable if they…
Can be achieved consistently.
These independent data sets should be compared ti determine
The reliability of results.
Discrete and continuous variables give rise to…
Qualitative, quantitative or ranked data.
Qualitative data?
Subjective and descriptive
Quantitative data?
Can be measured objectively, usually with a numerical value.
Ranked data?
Refers to data transformation in which numerical values are replaced by their rank when the database sorted from lowest to highest.
The type of variables being investigated has consequences for any…
Graphical display or statistical tests that may be used.
What is the mean
Average of numbers
What is the median?
The middle number
What is the mode?
The most frequent number.
What is the range?
Minimum and maximum number.
What is the interquartile range?
Measure that indicates the extent to which the central 50% of values within the data are dispersed. It is based upon and related to the median.
What are boxplots?
They show variation within and between data sets.
What are error bars?
Lines through a point on a graph that show the variation within the data.
What does statistical significance mean?
That results that are seen are most likely not due to chance or sampling error.
It is unlikely to be due to chance alone.
Correlation exists if?
There is a relationship between 2 variables.
Correlation is…
An association and does not only 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.
When does positive correlation exist?
When an increase in 1 variable is accompanied by an increase in the other variable.
When does negative correlation exist?
When an increase in 1 variable is accompanied by a decrease in the other variable.
Strength of correlation is proportional to…
Spread of values from line of best fit.
What is a confounding variable
Any factor affecting the dependent variable that is not the independent variable
