Experimental design
-
Upload
learning-development-centre -
Category
Technology
-
view
568 -
download
1
description
Transcript of Experimental design
![Page 1: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/1.jpg)
Experimental design
Dr Richard GoodeySEMS
4/5/2012 Researcher’s Development Day
![Page 2: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/2.jpg)
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 experiment
4/5/2012 Researcher’s Development Day
![Page 3: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/3.jpg)
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
![Page 4: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/4.jpg)
Results
• Have we answered the question?4/5/2012 Researcher’s Development Day
10 20 30 40 50 60 70 80 90 1000
20
40
60
80
100
120
Temperature (°C)
Vol o
f car
bon
diox
ide
(cc)
![Page 5: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/5.jpg)
General model
4/5/2012 Researcher’s Development Day
Process
x1 x2 xn
z1 z2 zn
Input Output
Uncontrollable factors
Controllable factors
![Page 6: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/6.jpg)
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 pressure
4/5/2012 Researcher’s Development Day
![Page 7: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/7.jpg)
Basic principles
• Replication– Not to be confused with repeated measurement
• Randomisation– Design against unknown nuisance factors
• Blocking– Eliminate or reduce known nuisance factors
4/5/2012 Researcher’s Development Day
![Page 8: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/8.jpg)
Guidelines for design
• Recognise and state the problem• Choose factors, range and levels• Select response variable• Design experiment• Perform experiment• Analyse data• Conclude and recommend
4/5/2012 Researcher’s Development Day
![Page 9: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/9.jpg)
Things to note
• Keep the design and analysis as simple as possible
• Practical vs statistical significance• Experiments are iterative and repetitive
4/5/2012 Researcher’s Development Day
![Page 10: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/10.jpg)
Experiment with a single factor
• Recognise and state the problem
• Choose factors, range and levels
• Select response variable
• What is the strength of fibres used to make shirts?
• Influenced by weight percent of cotton in fibre. Range between 10 and 40 percent. Levels 15, 20, 25, 30 and 35%
• Tensile strength
4/5/2012 Researcher’s Development Day
![Page 11: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/11.jpg)
Design experiment• Utilise replication and randomisation• Replication = 5 samples per level, total
number of tests therefore 25• Randomisation:
4/5/2012 Researcher’s Development Day
Cotton weight %
Experimental run number
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 25
![Page 12: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/12.jpg)
• Use a process to put those in random order
• Minimises unknown nuisance factors
4/5/2012 Researcher’s Development Day
Test sequence Run number Cotton weight %
1 8 20
2 18 30
…… …… ……
25 3 15
![Page 13: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/13.jpg)
Perform the experiment, collect data
• Now we need to perform some data analysis to assess significance etc
4/5/2012 Researcher’s Development Day
10 15 20 25 30 35 400
5
10
15
20
25
30
Cotton weight %
Tens
ile st
reng
th (p
si)
![Page 14: Experimental design](https://reader036.fdocuments.in/reader036/viewer/2022082803/54545c4daf7959564f8b571e/html5/thumbnails/14.jpg)
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 hypothesis
4/5/2012 Researcher’s Development Day