Unit 3: Key Area 2 Flashcards
How is validity achieved
Validity: variables controlled so that any measured effect is likely to be due to the independent variable.
How is reliability achieved
Reliability: consistent values in repeats and independent replicates.
How is accuracy achieved
Accuracy is when results of the average of sets of results are close to the true value
How is precision achieved
Precision: measured values are close to each other.
What is a pilot plan and what is it used for
Integral to the development of an investigation, a pilot study is used to help plan procedures, assess validity and check techniques
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
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 dependent variable
A dependent variable is the variable being measured in a scientific experiment.
What can both independent and dependent variables be?
Independent and dependent variables can be continuous or discrete
What are simple experiments
They only test one independent variable against the dependent variable
What are multifactorial experiments
More than one independent variable is tested against the dependent variable
A benefit and withdraw of conducting a simple experiment
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.
What do multifactorial experiments involve
A multifactorial experiment involves a combination of more than one independent variable or combination of treatments.
Describe Observational studies (also a benefit and cost)
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 (person) is not directly controlled by the investigator, for ethical or logistical reasons
Describe a confounding variable
Due to the complexities of biological systems,
other variables besides the independent
variable may affect the dependent variable
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 should be designed 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
Describe a randomised block
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
Control results are used for comparison with the results of treatment groups
Describe a negative control
The negative control provides results in the absence of a treatment.
Describe a positive control
A positive control is a treatment that is included to check that the system can detect a positive result when it occurs.
Describe the use of placebos
Placebos can be included as a treatment without the presence of the independent variable being investigated.
Describe 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.
Describe in vitro studies
In vitro refers to the technique of performing
a given procedure in a controlled
environment outside of a living organism
Describe in vivo studies
In vivo refers to experimentation using a whole, living organism
Give examples of in vitro
Examples of in vitro experiments: cells growing in culture medium, proteins in solution, purified organelles.
Advantage and Disadvantage of in vitro
Advantage - no harm to the organism being tested on
Disadvantage - may not give exactly the same effect as if carried out in a living organism
Describe sampling
Where it is impractical to measure every individual, a representative sample of the population is selected
Advantage and Disadvantage of in vivo
Advantage - will give an indication of the effect of the experiment in a living organism
Disadvantage - may harm the organism being tested on
What determines the sample size
- The extent of the natural variation within a population determines the appropriate sample size
- More variable populations require a larger sample size
- A representative sample should share the same mean and the same degree of variation about the mean as the population as a whole
Describe random sampling
In random sampling, members of the population have an equal chance of being selected.
Describe systematic sampling
In systematic sampling, members of a population are selected at regular intervals.
Describe stratified sampling
In stratified sampling, the population is divided into categories that are then sampled proportionally.
How can the natural variation in a biological material be determined
What will give an indication of the true value being measured
The natural variation in the biological material being used can be determined by measuring a sample of individuals from the population
The mean of these repeated measurements
will give an indication of the true value being
measured
What is the range of values and what does it mean if there is a narrow range
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
How can the reliability of measuring instruments or procedures be determined
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 indicate
The variation observed indicates the precision of the measurement instrument or procedure but not necessarily its accuracy
Why should independent replication be carried out
Independent replication should be carried out to produce independent data sets. This allows the results to be more valid and allow other scientists to try and replicate the trends obtained
How can the overall results be considered reliable
Overall results can only be considered reliable if they can be achieved consistently.
How to determine the reliability of the results from the independent data
These independent data sets should be
compared to determine the reliability of the
results
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.
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 factor affects the type of graph drawn or statistical test carried out
The type of variable being investigated has
consequences for any graphical display or
statistical tests that may be used
eg. discrete - bar graph
continuous - hysmean graph (bell-shaped)
How do you calculate the mean
Mean - total data added together divided by the number of data
How do you calculate the median
Median - the number in the middle when the data is numbered from lowest to the highest
How do you calculate the mode
Mode is the data that comes up the most frequent
When does correlation exist
Correlation exists if there is a relationship
between two variables
Describe a 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
Describe a positive correlation
A positive correlation exists when an increase in one variable is accompanied by an increase in the other variable.
Describe a negative correlation
A negative correlation exists when an increase in one variable is accompanied by a decrease in the other variable.
What does the strength of correlation depend on
Strength of correlation is proportional to spread of values from line of best fit.
What do error bars show
Error bars show the degree of variation around the mean. Long error bars equal a large degree of variation
Overlapping error bars do not show a significant effect of the independent variable
The error bars of the experiment are usually compared to the controls to check for significance
What is causation
causation is when the independent variable is known to affect the dependent variable
Are causation and correlation always linked
Correlation is an association and does not automatically imply causation
Causation only exists if the changes in the independent variable are know to cause changes to the dependent variable
