Experimental design              Dr Richard Goodey                     SEMS4/5/2012         Researcher’s Development Day
What is an experiment?• A test      – To find out something about a process      – More specifically, usually a series of ...
A simple example• What is the effect of temperature on the rate  of reaction between limestone and acid?• 2HCl + CaCO3 -> ...
Results                                        120                                        100           Vol of carbon diox...
General model                      Controllable factors                     x1     x2                       xn           I...
Our simple experiment………?•   Temperature control•   Concentration of acid•   Volume of acid•   Mass of limestone•   Size o...
Basic principles• Replication      – Not to be confused with repeated measurement• Randomisation      – Design against unk...
Guidelines for design•   Recognise and state the problem•   Choose factors, range and levels•   Select response variable• ...
Things to note• Keep the design and analysis as simple as  possible• Practical vs statistical significance• Experiments ar...
Experiment with a single factor• Recognise and state the           • What is the strength of  problem                     ...
Design experiment• Utilise replication and randomisation• Replication = 5 samples per level, total  number of tests theref...
• Use a process to put those in random order           Test sequence   Run number                     Cotton weight %     ...
Perform the experiment, collect data                                    30                                    25          ...
Summary• Performing an experiment is maybe not so  straightforward as it seems?• Careful planning will minimise:      – In...
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Experimental design

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Session 2B from City University London's Researchers' Development Day, held on Friday 4th May 2012.

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Experimental design

  1. 1. Experimental design Dr Richard Goodey SEMS4/5/2012 Researcher’s Development Day
  2. 2. What is an experiment?• A test – To find out something about a process – More specifically, usually a series of tests• Something we do all the time in our everyday lives• In this context, most relevant to physical and social sciences• In these fields, most PhD candidates and researchers do some sort of experiment4/5/2012 Researcher’s Development Day
  3. 3. A simple example• What is the effect of temperature on the rate of reaction between limestone and acid?• 2HCl + CaCO3 -> CaCl2 + H2O + CO2• So this should be simple?• Add limestone to acid, measure the volume of gas produced in one minute (e.g.)4/5/2012 Researcher’s Development Day
  4. 4. Results 120 100 Vol of carbon dioxide (cc) 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 Temperature (°C)• Have we answered the question?4/5/2012 Researcher’s Development Day
  5. 5. General model Controllable factors x1 x2 xn Input Process Output z1 z2 zn Uncontrollable factors4/5/2012 Researcher’s Development Day
  6. 6. Our simple experiment………?• Temperature control• Concentration of acid• Volume of acid• Mass of limestone• Size of limestone particles• Mechanism for measuring gas volume and time• Purity of reagents• Atmospheric pressure4/5/2012 Researcher’s Development Day
  7. 7. Basic principles• Replication – Not to be confused with repeated measurement• Randomisation – Design against unknown nuisance factors• Blocking – Eliminate or reduce known nuisance factors4/5/2012 Researcher’s Development Day
  8. 8. Guidelines for design• Recognise and state the problem• Choose factors, range and levels• Select response variable• Design experiment• Perform experiment• Analyse data• Conclude and recommend4/5/2012 Researcher’s Development Day
  9. 9. Things to note• Keep the design and analysis as simple as possible• Practical vs statistical significance• Experiments are iterative and repetitive4/5/2012 Researcher’s Development Day
  10. 10. Experiment with a single factor• Recognise and state the • What is the strength of problem fibres used to make shirts?• Choose factors, range • Influenced by weight and levels percent of cotton in fibre. Range between 10 and 40 percent. Levels 15, 20, 25, 30 and 35%• Select response variable • Tensile strength4/5/2012 Researcher’s Development Day
  11. 11. Design experiment• Utilise replication and randomisation• Replication = 5 samples per level, total number of tests therefore 25• Randomisation: Cotton Experimental run number weight % 15 1 2 3 4 5 20 6 7 8 9 10 25 11 12 13 14 15 30 16 17 18 19 20 35 21 22 23 24 254/5/2012 Researcher’s Development Day
  12. 12. • Use a process to put those in random order Test sequence Run number Cotton weight % 1 8 20 2 18 30 …… …… …… 25 3 15• Minimises unknown nuisance factors4/5/2012 Researcher’s Development Day
  13. 13. Perform the experiment, collect data 30 25 Tensile strength (psi) 20 15 10 5 0 0 5 10 15 20 25 30 35 40 Cotton weight %• Now we need to perform some data analysis to assess significance etc4/5/2012 Researcher’s Development Day
  14. 14. Summary• Performing an experiment is maybe not so straightforward as it seems?• Careful planning will minimise: – Inaccuracy – Time wasted• Some level of statistical analysis will be required to prove or disprove your hypothesis4/5/2012 Researcher’s Development Day

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