Experimentation Flashcards
What is validity?
Variables are 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 true value
What is precision?
Measured variables are close to each other
What are pilot studies?
Small scale preliminary studies which aim to investigate whether clinical
Pilot studies are integral to the development of an investigation and used to help…
Plan procedures
Assess validity
Check techniques
(allows evaluation and modification of experimental design)
The use of a pilot study…
Can ensure n appropriate range of values for the independent variable
Allows investigator to establish the number of repeat measurements required to give a representative value for each independent datum point
Why are the use of pilot studies necessary?
To avoid wasting significant time and money on full-scale investigations using flawed experimental methods
What is the experimental treatment group compared to?
Control group
What are variables?
Factors that can be controlled, changed or measured in an experiment
3 types of variables
Independent
Dependent
Confounding
An independent variable is…
Changed deliberately to determine if it has an effect on the outcome of the experiment
A dependent variable is…
Measured to determine if changing the the independent variable has an effect
Experiments involve the manipulation of…
Independent variable by the investigator
Variables can be…
Discrete- have a finite range of values that allow placement into groups
Continuous- change gradually from one extreme to another, potentially infinite number of possible values
What is a simple experimental design?
1 independent variable is changed e.g. lab based studies
What is a multi-factorial experimental design?
More than 1 independent variable is changed e.g. field studies and whole organism studies
Advantages of simple experimental design
Simpler experimental design
Variables tightly controlled
Results easy to interpret and analyse
Disadvantages of simple experimental design
Difficult to extrapolate results to whole organisms/environments
Not suitable for testing complex hypothesis
Advantages of multifactorial experimental design
Allows experimentation pf complex interactions
Allows generalisations to be made
Results are applicable to study organisms/environments
Disadvantages of multifactorial experimental design
More complex and time consuming
Difficult to control all variables
Complex analysis of data
What are observational studies?
When a variable that already exists within the study population is selected and considered to be the independent variable (no truly independent variable)
Observational studies are good at…
Detecting correlation, but since the do not directly test a hypothesis, they are less useful for determining causation
What is a confounding variable?
A variable other than the independent variable that may affect the dependent variable
Due to the complexities of biological systems…
Other variables besides the independent variable may affect the dependent variable
What should a valid experimental design do to confounding variables?
Hold the constant if possible, or at least monitored so that their effect on the results can be accounted for in analysis
What is used if confounding variables cannot be easily controlled?
Random block design (subjects are blocked randomly)
What does random block design involve?
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
Why are control groups used?
Results used for comparison with the results of treatment groups
What are negative controls?
Provides data for what happens on the absence of treatment, carried out to check false positive results are not occurring and should show dependent variable remains stable within an expected range the the independent variable is absent/constant
What causes unexpected results from a negative control?
Confounding variable not adequately controlled
What are positive controls?
Provides results/data to prove that the experimental design can detect a positive result when it occurs, carried out to check whether false negative results are occurring
What causes no effect on dependent variable from a positive control?
Invalid experimental design so refinement is required
What is a placebo control?
Control for patients’ expectations?
What is the placebo effect?
A measurable change in the dependent variable as a result of the patients’ exceptions rather than changes in the independent variable
Placebos are included as a treatment without the presence of the…
Independent variable being investigated (patient is unaware if they are receiving treatment or placebo)
What is an in vivo study?
Experimentation using a whole living organism
What is an in vitro study?
Procedure performed in a controlled environment outside of a living organism
Advantages of in vivo studies
Provide data for effects in whole organisms
Allows study of complex interactions
Disadvantages of in vivo studies
Expensive and time consuming
Ethical and legislative concerns
Difficult to control confounding variables
Results difficult to interpret
Difficult to prove causation
Advantages of in vitro studies
Simpler and less expensive
Easier to control confounding variables
Interpretation of results is simpler
Can demonstrate correlation and causation
Disadvantages of in vitro studies
Difficult to extend results to whole organism or different species
Difficult to model complex interactions
When it is impractical to measure every individual…
A representative sample of the population is selected
What determines appropriate sample size?
Extent of natural variation within a population (more means larger)
A representative sample should share the same…
Mean and degree of variation about the mean as the population as a whole
3 types of sampling
Random
Systematic
Stratified
What is random sampling?
Member of the population have an equal chance of being selected, should use random number tables or generators to select samples, used for very large areas/populations with relatively uniform distributions
What is systematic sampling?
Members of the population are selected at regular intervals
What is stratified sampling?
Population is divided into categories that are them sampled proportionally, used when population is not uniform
Variation in experimental results may be due to…
Reliability of measurement method and/or inherent variation in species
Variation in results can be influenced by…
Precision and accuracy of repeated measurements
How can the reliability of measuring instruments/procedures be determined?
Repeated measurements/readings of an individual datum point
How can natural variation in the biological material being used be determined?
Measuring a sample of individuals from the population
The mean of repeated measurements gives an…
Indication of the true values being measured
The range of values is a measure of…
Extent of variation in the results (narrow range=low variation)
What is independent replication?
Involves repeating the whole experiment
Independent replication should be carried out to produce…
Independent data sets to be compared to determine reliability of results, overall results can only be considered reliable if they can be achieved consistently
2 types of variation
Discrete- limited number of possible types of characteristic allowing individuals to be placed into groups
Continuous- describes
What is qualitative data?
Data which is subjective and descriptive, difficult to measure directly and analyse
Presented in a bar graph or pie chart
What is quantitative data?
Data which can be measured objectively, usually with a numerical value,easier to analyse
Presented in a line graph, scatter graph or histogram
What is ranked data?
Data transformation in which numerical values are replaced by their rank when data is sorted from highest to lowest
Presented in a bar graph
Type of variable being investigated has consequences for any…
Graphical display or statistical tests that may be used
What is the mean?
Average value for the data
What is the median?
Middle value for data
What is the mode?
Most common value in the data
What are error bars?
Graphical representation of the variability of data, used on graphs to indicate the errors/uncertainty in a repeated measurement (lines through a point on a graph)
What do smaller error bars indicate?
Less variable data
If error bars do not overlap…
Statistically significant results, allows comparison of results and method is valid
If error bars overlap…
Results are not statistically significant and method may be invalid
What is correlation?
Relationship between two variables where they both follow the same pattern
Correlation is an… it does not imply…
Association, causation
What is a positive correlation?
Exists when an increase in one variable is accompanied by an increase in the other variable
What is a negative correlation?
exists when an increase in one variable is accompanied by a decrease in the other variable
Strength of correlation is proportional to…
Spread of values from line of best fit
Why is the independent variable not directly controlled by investigator in observational studies?
Ethical or logistical reasons
