experimental design n.
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EXPERIMENTAL DESIGN

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EXPERIMENTAL DESIGN

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  1. Research Support Unit EXPERIMENTAL DESIGN • CONCEPTS • GUIDELINES • A FREE TOOL (IN AFRICA)

  2. Research Support Unit When ? • As in any research : after a problem analysis

  3. Research Support Unit What is research ? Many visions

  4. Research Support Unit What is research ? Quid est veritas ? What is truth ?

  5. Research Support Unit What is research ? • Touch of philosophy, strategy, … • In our context something like: To solve a problem in the development area concerning livelihoods and the environment.

  6. Research Support Unit How to do research ? • Der Logik der Forschung • 1934 • Sir Karl Popper (1902 – 1994) • In science, there is no absolute truth • There exist a body of ‘objective knowledge’ • This is constantly being questioned, modified, …

  7. Research Support Unit GUIDELINE 1 • READ • Read a lot • Read different subjects • Read different authors • Read from different influence zones (geopolitical, language, …) • Read also the old stuff

  8. Research Support Unit GUIDELINE 1

  9. Research Support Unit GUIDELINE 2 • TALK • Discuss with colleagues, supervisors, experts, …

  10. Research Support Unit OTHERWISE • If you don’t compare your ideas with the objective body of knowledge ….. • …… you’re NOT doing research.

  11. Research Support Unit Logical framework for the scientific research process • Observations • Problem analysis • Data collection • Investigation • Interpretation

  12. Research Support Unit Examples of observations • Phenomena and patterns: You observe some trees are bigger than others • What if-questions: « What if I would apply the theories of vegetation ecology on trees in an agricultural landscape organised in use groups ? » • Combination of observations and theories: Application of theories of natural forest regeneration developed during research in South America, in a Central African situation and observation of different outcomes.

  13. Research Support Unit Logical framework for the scientific research process

  14. Research Support Unit Objectives drive the study Study Objectives give details on what will be investigated to be able to reject or accept the research question with a specified probability. They determine: • 1. Treatments • 2. Layout • 3. Measurements

  15. Research Support Unit OBJECTIVESDRIVETHESTUDY !!!!

  16. Research Support Unit Objectives must be • Clear • Complete • Relevant How do they fit into the strategy? • Capable of being met by some type of study: an experiment, a survey, several experiments, …

  17. Research Support Unit Objectives must be • Axiom (known theory): clothes can be cleaned • Research question: Can they be cleaned using water and a washing powder ? • Study objectives: TOSS or OMO ? JóL

  18. Research Support Unit Objectives: Real World example • Concept: improved fruit trees • Research question:which one is the best ? • Objective: To evaluate 4 improved mango varieties JóL

  19. Research Support Unit Objectives: Real World example To determine whether the survival and growth rates, during the first two years, of improved mango varieties (Kent, Van Dyke, Tommy Atkins and Sensation) can be brought up to the level of the local variety by using a higher level of management (manure and water), when these trees are grown in crop fields of the coffee zone of Embu , Kenya.

  20. Research Support Unit GUIDELINE 3 • WRITE STUDY OBJECTIVES DOWN IN A STUDY PROTOCOL • Reference or number • Title • Location • Investigators and people involved in data collection • Background and justification • Study objectives • Methods • Implementation plan • References • Version • (Info somewhere on CD and in RSU course material)

  21. Research Support Unit GUIDELINE 3 • Importance of a study protocol • Basically, it helps in focusing • On the research questions • On the data • On a critical research approach • Also • Sharing • Continuity • Archiving (cfr. Audit-trail of data management course)

  22. Research Support Unit Objectives determine • Treatments: varieties, management • Layout: in crop fields of the coffee zone of Embu • Measurements: survival and growth rates during first two years

  23. Research Support Unit Key treatment concepts • Comparisons (contrasts) • Controls • Factorial treatment structure

  24. Research Support Unit Treatment concepts : contrasts • Objectives => hypothesis => defines contrast • each hypothesis corresponds to a contrast => each contrast determines a treatment

  25. Research Support Unit Treatment concepts : contrasts • In the mango example: • Improved variety + management vs local • Improved variety vs improved variety +management • => 3 treatments • Local • Improved variety • Improved variety + management

  26. Research Support Unit Treatment concepts : controls • Control = baseline • Depends; not necessarily zero input, do nothing, farmer practices, … • Example: Study of effect of fertilizer on crop yield of X on very poor soils • What could be control here ? • Also: controls must allow us to eliminate as many artifacts as possible introduced by our experimental procedure • Example: injected – not injected

  27. Research Support Unit Treatment concepts : factorial treatment structure • Example: to examine the influence of variety, the application of an insecticide and the application of a fungicide on the yield of maize

  28. Research Support Unit Treatment concepts : factorial treatment structure • Possibility 1

  29. Research Support Unit Treatment concepts : factorial treatment structure • Possibility 1: • Effect of the variety = difference between treatment B and A • Effect of the insecticide = difference between treatment C and A • Effect of the fungicide = difference between D and B • VALID, but ONLY if you are willing to accept that the effect of each factor is the same at all levels of the other factors

  30. Research Support Unit Treatment concepts : factorial treatment structure • Factorial structure:

  31. Research Support Unit Treatment concepts : factorial treatment structure • Factorial structure: • Main effects • Interactions = For instance “Does using an insecticide has the same effect on both varieties? “

  32. Research Support Unit Layout concepts • Replication • Randomisation • Blocking

  33. Research Support Unit Layout • What are the units or experimental objects • How many do we need ? • Where ? • Which one gets which treatment ? • ….

  34. Research Support Unit Layout concept : Replication • Tree number 43 of variety Kent in the coffee zone of Embu that was given extra manure and water has grown 37 cm at the end of the second year • Tree number 17 of variety Tommy Atkins in the coffee zone of Embu that received no extra water and manure has grown 15 cm at the end of the second year • What statistical analysis do we need to carry out on this comparison ?

  35. Research Support Unit Layout concept: Replication • Replication => measuring variability • Only then possible • to add a measure of precision • or test a hypothesis • Appropriate replication at each scale !

  36. Research Support Unit Layout concept: Randomisation • To avoid systematic error

  37. Research Support Unit Layout concept: Blocking • Basically, we split up the variability into variability between blocks and variability between treatments • => able to get more precise comparison of treatments • Units in the same block give similar response when subject to same treatment

  38. Research Support Unit Layout concept: Blocking • “Block” ? • Can be concentric (around light source) • Same management • for instance always the same technician for a given block • Aim to harvest a whole number of blocks in one day • … • Randomized block: gradient in 1 direction • Latin square: gradient in 2 directions • Both: number of units in each block is the same and equal to the number of treatments

  39. Research Support Unit Measurement concepts • Response measurements meet primary objectives growth, yield, disease, farmers ranking,… • Explanatory measurements help understand variation in the response rainfall, soil type, farm income, planting method • Measurements can be made at any level in the layout hierarchy • Choose a suitable measurement tool

  40. Research Support Unit Example Example: Compare rooting of 3 clones. 50 cuttings of each clone in a propagator 4 possible layouts Each use the same number of cuttings and the same space in the propagator

  41. 1 2 Research Support Unit 3 4

  42. Research Support Unit JóL Which do you prefer?

  43. Research Support Unit • Within units • Has to do with s.e. of a treatment mean = sqrt(s2/n) • More precise estimation of means • Between units • Rule of thumb : 2 to 4 replicates • Sqrt(1/2) = 1/1.7  sqrt(1/4) = 1/2 • Not so much difference; more = expensive • Has to do with number of d.f. of error term: • Rule of thumb: 10 to 20 d.f. • This error mean square is used in the F-test in an ANOVA

  44. Research Support Unit Fancy designs • Graeco-Latin = square or queer ?

  45. Research Support Unit Fancy designs • Problem in tree domestication is often that quite a large number of varieties are tested. • Randomized complete block designs not possible (too expensive) • Principle = omitting treatments in blocks

  46. Research Support Unit So what ? • Logical framework for the scientific research process = cycle • Ask yourself after each cycle: so what ? • Relevant, something new, …. ?

  47. Research Support Unit So what ? • Complex statistical analysis is not synonym of relevant high quality research

  48. Research Support Unit FINAL GUIDELINE • USE COMMON SENSE • THINK CRITICAL • BALANCE THEORY AND PRACTICE

  49. Research Support Unit A Free Tool • If you’re based in Africa • For non-commercial use