AH Biology: Unit 3 Investigative Biology Topic 2- Experimentation: Pilot Studies

Topic outline a)Pilot study b)Variables c)Experimental design d)Controls e)Ensuring reliability

a) Pilot study what you need to know The use of a pilot study to develop and/or practice protocols in order to ensure validity of experimental design, check effectiveness of techniques, find a suitable range of values for the independent variable, identify and control confounding variables, identifying suitable numbers of replicates. Integral to the development of an investigation, a pilot study is used to help plan procedures, assess validity and check techniques.

a) Pilot study what you need to know 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. The use of a pilot study can ensure an appropriate range of values for the independent variable to avoid results for the dependent variable ending up ‘off the scale’. In addition, it allows the investigator to establish the number of repeat measurements required to give a true value for each independent datum point. A pilot study can also be used to check whether results can be produced in a suitable time frame.

Pilot studies In any investigation the viability of a course of research is fundamentally important. The viability of any piece of research is usually investigated by a pilot study.

Pilot studies The use of a pilot study is to: – Develop and practice protocols in order to ensure the validity of experimental design. – Check effectiveness of techniques – Find a suitable range of values for the independent variable. – Identify and control confounding variables. – Identifying suitable numbers of replicates. This allows evaluation and modification of experimental design.

Pilot studies A pilot study can be used to develop a new protocol or to enable an investigator to become proficient in using an established protocol. The use of a pilot study can ensure an appropriate range of values for the independent variable to avoid results for the dependent variable ending up ‘off the scale’. In addition, it allows the investigator to establish the number of repeat measurements required to give a true value for each independent datum point. It can also be used to check whether results can be produced in a suitable time frame.

Activity- Look at the examples in the scholar notes page 18/19

Pilot studies 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. [CC-BY-2.5 ( via Wikimedia Commons

Pilot studies 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?

Pilot studies – Can stocks be sourced and maintained in a school laboratory? Yes, eg Blades Biological bio.co.uk bio.co.uk – How can we measure the dependent variable? Heart rate can be measured using a microscope but the way this is done will require careful consideration. – Try it yourself with this link: watch?v=MJCnZ0pB3q4 Heart [CC-BY-2.5 ( via Wikimedia Commons

Pilot studies Heart rate measurement Students will need to pilot whether they can measure heart rate accurately and for how long. – The heart contraction can be visualised under a normal laboratory microscope and measured using a hand tally. There are many potential issues which need to be resolved by researching and developing this technique. – Daphnia are very mobile therefore how can they be kept in the field of view? Restricting fluid volume and using inert gels have been tried with varying success. – Does manipulating Daphnia onto a slide for viewing cause an increase in heart rate? Yes – Does prolonged exposure to the heat of a microscope lamp affect heart rate? Yes How do we measure and establish resting heart rate in light of the above? – Good question!

Pilot studies We have raised the issue of several confounding variables and a pilot study or studies will be required to resolve this before the model is suitable for use in an investigation. Once the learner has overcome this issue the following also need to be addressed: What range of the dependent variable can be used and how can it be delivered to the Daphnia and with what accuracy? – Research and trial and error. Any manipulation of the Daphnia will result in increased heart rate. How can this be controlled and limited? – It may be necessary to take readings over a time base compared to a control that has water added rather than ethanol. Any manipulation effect can then be observed and accounted for in the experiment. – 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? This may involve very accurate measurement of the fluid the Daphnia is in.

Pilot studies Data It should be anticipated that if all of the previous constraints are overcome, and they can be, the learner will collect data. But what form could this take? It is to be assumed that dose curves of heart rate against ethanol concentration will be produced. These should be compared against control groups. How many samples should be taken? – At least four or five different values of ethanol concentration should be used and replicated at least twice. – This also raises the issue of sample size, ie how many Daphnia should be used per concentration per replicate to be valid. The answer is as many as you can manage within your time constraints but a suggestion of a minimum of five or six per concentration/replicate should be attempted. – Remember: an average of two Daphnia is still a poor sample.

Pilot studies If you can solve all of the previous issues you will be able to use Daphnia magma as a laboratory model for physiology experiments. Remember one final thing: it is still a crustacean, not a human! Care needs to be taken to avoid over-extrapolation to humans or other vertebrates.

a) Pilot study what you need to know The use of a pilot study to develop and/or practice protocols in order to ensure validity of experimental design, check effectiveness of techniques, find a suitable range of values for the independent variable, identify and control confounding variables, identifying suitable numbers of replicates. Integral to the development of an investigation, a pilot study is used to help plan procedures, assess validity and check techniques.

a) Pilot study what you need to know 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. The use of a pilot study can ensure an appropriate range of values for the independent variable to avoid results for the dependent variable ending up ‘off the scale’. In addition, it allows the investigator to establish the number of repeat measurements required to give a true value for each independent datum point. A pilot study can also be used to check whether results can be produced in a suitable time frame.