Describe the genetic issue with human experiments and how it can be combated.
- large genetic variation within a population - many people will respond differently
minimised by:
- large sample size (100s-1000s)
- using identical twins
- randomly selected to avoid bias (most of the time)
Describe the ethical considerations involved in human experiments.
Safety
- minimally invasive, minimal harm (risk assessment)
Consent
- participants must be informed consent in writing (e.g. for storage of specimens long term)
- participants may be given a placebo: they must agree to this
Conditions
- confidentiality around releasing info on the study
- participants can withdraw at any time
- the findings must be shared with participants
- if the medication is successful, the placebo group must be given access after the trial
placebo
- a non-medicated version of the drug
- used to test the effectiveness of treatments
- participants do not know which version they received
- researchers can measure if the drug works by comparison between the placebo and drug
- if they both have the same reaction, the drug is deemed ineffective
placebo effect
- when something with NO known therapeutic effect actually has an effect
- people believe that they will feel better, and therefore they feel better
- minds create the medicine
- it can have a measurable effect on the body if believed strongly enough
single blind vs double blind
- Single blind: participant doesn’t know if they have the placebo/drug, researchers know
- Double blind: neither participant nor researcher knows
Describe the ethical considerations involved in animal experiments.
- all animals have intrinsic value
- some animals have strict guidelines (fish, birds, mammals, octopus etc)
Conditions
- must have approval to test on animals
- must cause minimal habitat disruption + protect biodiversity
- must respect + provide care for animals
- must know/consider alternatives for animal testing
- suffering can only be caused if counterbalanced by a substantial benefit for animals, humans, or the environment
- must be transparent with findings of study
Describe the aim of risk assessments in experimental design.
Crucial to determine possible danger to the:
- experimenter
- subjects
- environment
- property
Considers how they can be avoided, reduced + dealt with.
independent vs dependent variables
Independent: the factor that is deliberately changed/manipulated
Dependent: the factor that is measured
Describe the elements of a controlled experiment.
A controlled experiment:
- tests the validity of the hypothesis
- is repeatable and reliable
- includes a control group
- has only one DV and IV
- only changes the IV between treatments
- controls all other variables where possible
control vs experimental groups
Control: the group that is the standard of comparison
- a ‘natural’ or baseline state
- no treatment/manipulation
Experimental: the group that is given the treatment (IV conditions changed)
Describe the terminology of an experimental setup using plants with different concentrations of fertiliser as an example.
- Treatment groups: the different variations of the IV (different concentrations of fertiliser)
- Sample size: the number of elements in each treatment group (15 plants for each of the three differing concentrations)
- Trial: the entire experiment with all IV variations (all 45 plants)
- Replication: a repeat of the trial (another 45 plants)
- Repeat: a total repeat of all the trials, the entre experiment again
Describe the process of writing an experimental report.
- hypothesis
- procedure (DV, IV, controlled variables, apparatus, method)
- evaluation (validity, reliability, risk/ethics)
Describe the elements of writing an experimental evaluation.
Validity (accuracy)
- control group
- fixed variables
- placebos/bias
Reliability (consistency)
- sample size
- no. of trials
- repeatability
Risk/ethics
- potential harm to humans/organism/environment
- consent
- describe improvements for each limitation discussed
Describe the elements of a good hypothesis.
- only 1 IV
- definite statement (not a question)
- testable via experimentation
- the ‘effect’ on the DV is quantitively measurable
- shows direction in relationship between IV + DV
Describe the elements of a data table for recording experimental findings.
Consider
- how many IV treatments + trials?
- is it being repeated?
- is the data being averaged?
Elements
- title
- IV usually on left
- label columns with variable names + units
- at least 3 trials
- always average
- if used, TIME will usually take left hand side - IV then placed across top
Describe the 3 types of experimental hypotheses.
Manipulation
- when the effect of manipulating a variable is being investigated (e.g. as light intensity increases, as does the Phs rates of plant A)
Choice
- when investigating species preferences (e.g. Bird species A will choose tree species X when nesting)
Observation
- when organisms are being observed in their natural environment + conditions cannot be changed (e.g. fern abundance is increased by a higher amount of canopy cover)
State the components required in a general exam question on experimental design.
- IV (state, units, briefly how manipulated)
- DV (state, units, how measured)
- Fixed V (at least 4)
- Control group!!!
- Trials (how many? what IV variations? increments between them?)
- Ethical considerations
State the types of improvements that can be made to an experiment to make it more reliable/valid.
- more trials (greater scale of testing)
- larger sample size (better identification of outliers, clearer trend)
- better control of fixed variables (specific)
- placebo/control group (deem effectiveness of drug through comparison)
