Unit 3 Investigative Biology
SQA
Success Criteria
 Explain the need for a pilot study in
terms of the dependent variable, the
independent variable, confounding
variables and replicates.
Pilot studies
Integral to the development of any
investigation, a pilot study is used to help
plan procedures, assess validity and
check techniques.
 This allows evaluation and modification
of experimental design.
 A pilot study can be used to develop a new
protocol or to enable an investigator to
become proficient in using an established
protocol.
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Pilot study example
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Daphnia magma is a fresh water crustacean often used in
laboratory studies of physiology or toxicity.
It is readily available and often used to measure the effect of
drugs such as caffeine and ethanol on heart rate.
Heart
Pilot studies


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How could we set up a pilot study to see if
Daphnia could provide a suitable laboratory model
to look at the effect of ethanol on heart rate?
The aim here is to raise questions about the
issues that may need to be resolved.
Planning questions:
 Can stocks be sourced and maintained in a
school laboratory?
 How can we measure the dependent variable,
heart rate?
 How can we alter and set ranges for the
independent variable, ethanol concentration?
Confounding Variables??!
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Due to the complexities of biological systems,
other variables besides the independent
variable may affect the dependent variable.
A confounding variable is therefore an
extraneous (“outside” ) variable that is linked
to both the independent and dependant
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 could they be?
Daphnia are very mobile therefore how
can they be kept in the field of view?
 Does manipulating Daphnia onto a slide
for viewing cause an increase in heart
rate?
 Does prolonged exposure to the heat of
a microscope lamp affect heart rate?
 How do we measure and establish
resting heart rate in light of the above?

Pilot studies
A pilot study will be required to resolve
this before the protocol is suitable for use
in an investigation.
 What range of the dependent variable can
be used and how can it be delivered to the
Daphnia and with what accuracy?
 If we are looking at concentrations of the
independent variable how can we be sure
of what dose actually is being delivered to
the Daphnia?

Pilot studies

How many samples should be taken?
 At least four different values of ethanol
concentration should be used and replicated at
least twice.
 This also raises the issue of sample size, i.e.
how many Daphnia should be used per
concentration per replicate to be valid?
 As many as you can manage within your time
constraints but a minimum of five per
concentration/replicate should be attempted.
 An average of two Daphnia is still a poor
sample.
Success Criteria
 Explain the need for a pilot study in
terms of the dependent variable, the
independent variable, confounding
variables and replicates.